diff --git a/100_Numpy_exercises.ipynb b/100_Numpy_exercises.ipynb
index ae49130..d5b1152 100644
--- a/100_Numpy_exercises.ipynb
+++ b/100_Numpy_exercises.ipynb
@@ -2,7 +2,7 @@
  "cells": [
   {
    "cell_type": "markdown",
-   "id": "c742d9cc",
+   "id": "bf79c78b",
    "metadata": {},
    "source": [
     "# 100 numpy exercises\n",
@@ -18,7 +18,7 @@
   },
   {
    "cell_type": "markdown",
-   "id": "4292e21c",
+   "id": "8536e059",
    "metadata": {},
    "source": [
     "File automatically generated. See the documentation to update questions/answers/hints programmatically."
@@ -26,7 +26,7 @@
   },
   {
    "cell_type": "markdown",
-   "id": "e1eba8a7",
+   "id": "e16ac60b",
    "metadata": {},
    "source": [
     "Run the `initialize.py` module, then for each question you can query the\n",
@@ -36,7 +36,7 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "1ca6f730",
+   "id": "a8453483",
    "metadata": {},
    "outputs": [],
    "source": [
@@ -45,7 +45,7 @@
   },
   {
    "cell_type": "markdown",
-   "id": "c6ed9243",
+   "id": "017db353",
    "metadata": {},
    "source": [
     "#### 1. Import the numpy package under the name `np` (★☆☆)"
@@ -54,14 +54,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "4dc18925",
+   "id": "68182a76",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "b4882d94",
+   "id": "46950f4f",
    "metadata": {},
    "source": [
     "#### 2. Print the numpy version and the configuration (★☆☆)"
@@ -70,14 +70,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "9a41fb2b",
+   "id": "2a9f5838",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "084258bf",
+   "id": "e3c20b3d",
    "metadata": {},
    "source": [
     "#### 3. Create a null vector of size 10 (★☆☆)"
@@ -86,14 +86,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "660c6b91",
+   "id": "8a758bcf",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "0b7ea863",
+   "id": "b15a879f",
    "metadata": {},
    "source": [
     "#### 4. How to find the memory size of any array (★☆☆)"
@@ -102,14 +102,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "ac12eeb3",
+   "id": "1cc3cbc5",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "399ac53c",
+   "id": "0a708990",
    "metadata": {},
    "source": [
     "#### 5. How to get the documentation of the numpy add function from the command line? (★☆☆)"
@@ -118,14 +118,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "8706e03d",
+   "id": "477e01f4",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "94fb58be",
+   "id": "0b16cd77",
    "metadata": {},
    "source": [
     "#### 6. Create a null vector of size 10 but the fifth value which is 1 (★☆☆)"
@@ -134,14 +134,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "618f340f",
+   "id": "4d9b5975",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "d577e66c",
+   "id": "782d4c77",
    "metadata": {},
    "source": [
     "#### 7. Create a vector with values ranging from 10 to 49 (★☆☆)"
@@ -150,14 +150,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "091a60f4",
+   "id": "5dbe1a08",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "bc9c60e2",
+   "id": "48d48f01",
    "metadata": {},
    "source": [
     "#### 8. Reverse a vector (first element becomes last) (★☆☆)"
@@ -166,14 +166,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "23978628",
+   "id": "3ed233e7",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "7454fb7b",
+   "id": "4fa39382",
    "metadata": {},
    "source": [
     "#### 9. Create a 3x3 matrix with values ranging from 0 to 8 (★☆☆)"
@@ -182,14 +182,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "28f9a38f",
+   "id": "c97757ec",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "caf21358",
+   "id": "da64551a",
    "metadata": {},
    "source": [
     "#### 10. Find indices of non-zero elements from [1,2,0,0,4,0] (★☆☆)"
@@ -198,14 +198,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "d390f4e1",
+   "id": "327f7adb",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "1dd829ac",
+   "id": "f89d9c9e",
    "metadata": {},
    "source": [
     "#### 11. Create a 3x3 identity matrix (★☆☆)"
@@ -214,14 +214,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "1dde894f",
+   "id": "ba625832",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "322aa74e",
+   "id": "7e44c6fa",
    "metadata": {},
    "source": [
     "#### 12. Create a 3x3x3 array with random values (★☆☆)"
@@ -230,14 +230,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "1f5c8d38",
+   "id": "1cb3dddf",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "82e8c932",
+   "id": "13c5928c",
    "metadata": {},
    "source": [
     "#### 13. Create a 10x10 array with random values and find the minimum and maximum values (★☆☆)"
@@ -246,14 +246,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "85c6a59d",
+   "id": "911c9b93",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "c78b3d5e",
+   "id": "3fa2e461",
    "metadata": {},
    "source": [
     "#### 14. Create a random vector of size 30 and find the mean value (★☆☆)"
@@ -262,14 +262,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "37149237",
+   "id": "323eb38a",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "c07320af",
+   "id": "73f7a549",
    "metadata": {},
    "source": [
     "#### 15. Create a 2d array with 1 on the border and 0 inside (★☆☆)"
@@ -278,14 +278,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "19897ca9",
+   "id": "e3a6807d",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "c6d094c4",
+   "id": "6d0c506f",
    "metadata": {},
    "source": [
     "#### 16. How to add a border (filled with 0's) around an existing array? (★☆☆)"
@@ -294,14 +294,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "9c05295e",
+   "id": "32ffee7b",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "6e00ebde",
+   "id": "d6ad1a9f",
    "metadata": {},
    "source": [
     "#### 17. What is the result of the following expression? (★☆☆)\n",
@@ -318,14 +318,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "5015d2a2",
+   "id": "ee7ff0f3",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "ffee7be0",
+   "id": "e3a7ba7f",
    "metadata": {},
    "source": [
     "#### 18. Create a 5x5 matrix with values 1,2,3,4 just below the diagonal (★☆☆)"
@@ -334,14 +334,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "2db510c1",
+   "id": "01d8e257",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "0c687bd7",
+   "id": "6d17ab5d",
    "metadata": {},
    "source": [
     "#### 19. Create a 8x8 matrix and fill it with a checkerboard pattern (★☆☆)"
@@ -350,30 +350,30 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "c7a51f78",
+   "id": "841373cd",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "46c55b45",
+   "id": "8837119b",
    "metadata": {},
    "source": [
-    "#### 20. Consider a (6,7,8) shape array, what is the index (x,y,z) of the 100th element?"
+    "#### 20. Consider a (6,7,8) shape array, what is the index (x,y,z) of the 100th element? (★☆☆)"
    ]
   },
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "d95d1406",
+   "id": "2c0d16f1",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "4898dddb",
+   "id": "ec788c9f",
    "metadata": {},
    "source": [
     "#### 21. Create a checkerboard 8x8 matrix using the tile function (★☆☆)"
@@ -382,14 +382,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "de7dc9d8",
+   "id": "0a4f919f",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "ef2963f0",
+   "id": "391791e0",
    "metadata": {},
    "source": [
     "#### 22. Normalize a 5x5 random matrix (★☆☆)"
@@ -398,14 +398,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "f92f76ce",
+   "id": "f6533d39",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "09390c44",
+   "id": "1e74d39e",
    "metadata": {},
    "source": [
     "#### 23. Create a custom dtype that describes a color as four unsigned bytes (RGBA) (★☆☆)"
@@ -414,14 +414,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "86bea398",
+   "id": "3f639d33",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "e8ff25fc",
+   "id": "78250c14",
    "metadata": {},
    "source": [
     "#### 24. Multiply a 5x3 matrix by a 3x2 matrix (real matrix product) (★☆☆)"
@@ -430,14 +430,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "bcb2fa2e",
+   "id": "9fe729cb",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "ce43c805",
+   "id": "51898680",
    "metadata": {},
    "source": [
     "#### 25. Given a 1D array, negate all elements which are between 3 and 8, in place. (★☆☆)"
@@ -446,14 +446,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "2b915f12",
+   "id": "51c90f2d",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "20696fea",
+   "id": "89e78048",
    "metadata": {},
    "source": [
     "#### 26. What is the output of the following script? (★☆☆)\n",
@@ -469,14 +469,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "89d43108",
+   "id": "b62e9d1c",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "9f3e3396",
+   "id": "ebd10810",
    "metadata": {},
    "source": [
     "#### 27. Consider an integer vector Z, which of these expressions are legal? (★☆☆)\n",
@@ -493,17 +493,17 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "fa6a4ad1",
+   "id": "6ada209f",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "99a826bb",
+   "id": "c0e940f8",
    "metadata": {},
    "source": [
-    "#### 28. What are the result of the following expressions?\n",
+    "#### 28. What are the result of the following expressions? (★☆☆)\n",
     "```python\n",
     "np.array(0) / np.array(0)\n",
     "np.array(0) // np.array(0)\n",
@@ -514,14 +514,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "f5178b8b",
+   "id": "820dc7a5",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "04270e58",
+   "id": "22713c3f",
    "metadata": {},
    "source": [
     "#### 29. How to round away from zero a float array ? (★☆☆)"
@@ -530,14 +530,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "7dcb8271",
+   "id": "a3e05c29",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "186af0bd",
+   "id": "f1ae2c2d",
    "metadata": {},
    "source": [
     "#### 30. How to find common values between two arrays? (★☆☆)"
@@ -546,14 +546,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "751ce3d6",
+   "id": "6801c73d",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "8dc246e6",
+   "id": "34a7bdee",
    "metadata": {},
    "source": [
     "#### 31. How to ignore all numpy warnings (not recommended)? (★☆☆)"
@@ -562,14 +562,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "882d5831",
+   "id": "befc60d1",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "46286b98",
+   "id": "37bc0973",
    "metadata": {},
    "source": [
     "#### 32. Is the following expressions true? (★☆☆)\n",
@@ -581,14 +581,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "35b2ee6a",
+   "id": "c70cbabe",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "c19f893b",
+   "id": "129c342d",
    "metadata": {},
    "source": [
     "#### 33. How to get the dates of yesterday, today and tomorrow? (★☆☆)"
@@ -597,14 +597,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "39f552e8",
+   "id": "8ba1badb",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "7507fb36",
+   "id": "42f8b2f9",
    "metadata": {},
    "source": [
     "#### 34. How to get all the dates corresponding to the month of July 2016? (★★☆)"
@@ -613,14 +613,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "23c538eb",
+   "id": "eb8ebe45",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "d62fba94",
+   "id": "252c43e2",
    "metadata": {},
    "source": [
     "#### 35. How to compute ((A+B)*(-A/2)) in place (without copy)? (★★☆)"
@@ -629,14 +629,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "b517ffa9",
+   "id": "f06ff615",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "0593c304",
+   "id": "486df8ea",
    "metadata": {},
    "source": [
     "#### 36. Extract the integer part of a random array of positive numbers using 4 different methods (★★☆)"
@@ -645,14 +645,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "9c7ad92e",
+   "id": "34b4fa08",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "e90b042b",
+   "id": "649e89f9",
    "metadata": {},
    "source": [
     "#### 37. Create a 5x5 matrix with row values ranging from 0 to 4 (★★☆)"
@@ -661,14 +661,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "7892b4b0",
+   "id": "663cc611",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "a2d7df8e",
+   "id": "3421e17f",
    "metadata": {},
    "source": [
     "#### 38. Consider a generator function that generates 10 integers and use it to build an array (★☆☆)"
@@ -677,14 +677,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "5f323469",
+   "id": "7336b8e4",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "064c68c0",
+   "id": "483dd554",
    "metadata": {},
    "source": [
     "#### 39. Create a vector of size 10 with values ranging from 0 to 1, both excluded (★★☆)"
@@ -693,14 +693,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "a179d69e",
+   "id": "c89b93e7",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "5682b5b3",
+   "id": "2d07be1c",
    "metadata": {},
    "source": [
     "#### 40. Create a random vector of size 10 and sort it (★★☆)"
@@ -709,14 +709,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "f5e5b511",
+   "id": "4f7cb3ad",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "c8831686",
+   "id": "6415f02e",
    "metadata": {},
    "source": [
     "#### 41. How to sum a small array faster than np.sum? (★★☆)"
@@ -725,14 +725,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "31c6ec4d",
+   "id": "bb0dd942",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "c39eed1e",
+   "id": "fe043549",
    "metadata": {},
    "source": [
     "#### 42. Consider two random array A and B, check if they are equal (★★☆)"
@@ -741,14 +741,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "c4bf0ba3",
+   "id": "3326a686",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "ffafa4aa",
+   "id": "cc08f71c",
    "metadata": {},
    "source": [
     "#### 43. Make an array immutable (read-only) (★★☆)"
@@ -757,14 +757,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "c237c0d2",
+   "id": "d5cc9dbe",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "86886e5e",
+   "id": "2002cb03",
    "metadata": {},
    "source": [
     "#### 44. Consider a random 10x2 matrix representing cartesian coordinates, convert them to polar coordinates (★★☆)"
@@ -773,14 +773,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "5146f04c",
+   "id": "58be72bc",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "50740a46",
+   "id": "b7109c9f",
    "metadata": {},
    "source": [
     "#### 45. Create random vector of size 10 and replace the maximum value by 0 (★★☆)"
@@ -789,14 +789,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "2c11ffdd",
+   "id": "f79e79a7",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "5979e3ee",
+   "id": "7d3131b9",
    "metadata": {},
    "source": [
     "#### 46. Create a structured array with `x` and `y` coordinates covering the [0,1]x[0,1] area (★★☆)"
@@ -805,30 +805,30 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "0747c0d6",
+   "id": "4f471afe",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "cd53abc3",
+   "id": "7c8c1fc5",
    "metadata": {},
    "source": [
-    "#### 47. Given two arrays, X and Y, construct the Cauchy matrix C (Cij =1/(xi - yj))"
+    "#### 47. Given two arrays, X and Y, construct the Cauchy matrix C (Cij =1/(xi - yj)) (★★☆)"
    ]
   },
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "2d14d9b7",
+   "id": "8fac7d28",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "37875f0d",
+   "id": "5795b4bd",
    "metadata": {},
    "source": [
     "#### 48. Print the minimum and maximum representable value for each numpy scalar type (★★☆)"
@@ -837,14 +837,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "1578e3fa",
+   "id": "b721f7ca",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "aa4ce1fd",
+   "id": "fb24674c",
    "metadata": {},
    "source": [
     "#### 49. How to print all the values of an array? (★★☆)"
@@ -853,14 +853,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "4f1e9847",
+   "id": "c81f1456",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "ae637202",
+   "id": "e6e1ae2f",
    "metadata": {},
    "source": [
     "#### 50. How to find the closest value (to a given scalar) in a vector? (★★☆)"
@@ -869,14 +869,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "c4546e5c",
+   "id": "73dd91cc",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "93157464",
+   "id": "c01f0ecf",
    "metadata": {},
    "source": [
     "#### 51. Create a structured array representing a position (x,y) and a color (r,g,b) (★★☆)"
@@ -885,14 +885,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "69c4b979",
+   "id": "fb8017ca",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "07ebafa2",
+   "id": "3b64a18b",
    "metadata": {},
    "source": [
     "#### 52. Consider a random vector with shape (100,2) representing coordinates, find point by point distances (★★☆)"
@@ -901,14 +901,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "2db3c3e5",
+   "id": "4b482822",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "fb93d503",
+   "id": "48413134",
    "metadata": {},
    "source": [
     "#### 53. How to convert a float (32 bits) array into an integer (32 bits) in place?"
@@ -917,14 +917,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "67231bf2",
+   "id": "5db64b6d",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "9c0ce40b",
+   "id": "0a532633",
    "metadata": {},
    "source": [
     "#### 54. How to read the following file? (★★☆)\n",
@@ -938,14 +938,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "aecef043",
+   "id": "8af4f753",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "bdfe9e5d",
+   "id": "f98713a6",
    "metadata": {},
    "source": [
     "#### 55. What is the equivalent of enumerate for numpy arrays? (★★☆)"
@@ -954,14 +954,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "bcc193c9",
+   "id": "64795f84",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "fa2e5fc9",
+   "id": "1abc7cc8",
    "metadata": {},
    "source": [
     "#### 56. Generate a generic 2D Gaussian-like array (★★☆)"
@@ -970,14 +970,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "7b94a92a",
+   "id": "42e3a5bc",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "465a1ea4",
+   "id": "0cf413ee",
    "metadata": {},
    "source": [
     "#### 57. How to randomly place p elements in a 2D array? (★★☆)"
@@ -986,14 +986,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "c2d1d13f",
+   "id": "dfc57e06",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "d75998b5",
+   "id": "215b6acc",
    "metadata": {},
    "source": [
     "#### 58. Subtract the mean of each row of a matrix (★★☆)"
@@ -1002,14 +1002,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "44c2043a",
+   "id": "dd1adef4",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "4f2e8b7a",
+   "id": "c0cf37e0",
    "metadata": {},
    "source": [
     "#### 59. How to sort an array by the nth column? (★★☆)"
@@ -1018,14 +1018,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "d0b80ded",
+   "id": "9336ca5f",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "be56980d",
+   "id": "c17fb213",
    "metadata": {},
    "source": [
     "#### 60. How to tell if a given 2D array has null columns? (★★☆)"
@@ -1034,14 +1034,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "6dc4eaf6",
+   "id": "7fdda78d",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "92e0b60c",
+   "id": "8aaab886",
    "metadata": {},
    "source": [
     "#### 61. Find the nearest value from a given value in an array (★★☆)"
@@ -1050,14 +1050,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "0b37b462",
+   "id": "973f8079",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "476bb933",
+   "id": "66a04e2e",
    "metadata": {},
    "source": [
     "#### 62. Considering two arrays with shape (1,3) and (3,1), how to compute their sum using an iterator? (★★☆)"
@@ -1066,14 +1066,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "33c8566d",
+   "id": "4b356632",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "64aea808",
+   "id": "f4427f7f",
    "metadata": {},
    "source": [
     "#### 63. Create an array class that has a name attribute (★★☆)"
@@ -1082,14 +1082,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "db81ac8b",
+   "id": "fe253212",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "fb0a4de3",
+   "id": "58be9dd4",
    "metadata": {},
    "source": [
     "#### 64. Consider a given vector, how to add 1 to each element indexed by a second vector (be careful with repeated indices)? (★★★)"
@@ -1098,14 +1098,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "4726a17d",
+   "id": "5c8bae42",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "ae1a4b8d",
+   "id": "7348abd0",
    "metadata": {},
    "source": [
     "#### 65. How to accumulate elements of a vector (X) to an array (F) based on an index list (I)? (★★★)"
@@ -1114,14 +1114,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "2d0f1ee4",
+   "id": "b3e33a5a",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "a5127520",
+   "id": "538e651c",
    "metadata": {},
    "source": [
     "#### 66. Considering a (w,h,3) image of (dtype=ubyte), compute the number of unique colors (★★☆)"
@@ -1130,14 +1130,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "546bc0a2",
+   "id": "57f2f02f",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "1eaa1407",
+   "id": "33c986d9",
    "metadata": {},
    "source": [
     "#### 67. Considering a four dimensions array, how to get sum over the last two axis at once? (★★★)"
@@ -1146,14 +1146,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "7823c50c",
+   "id": "a99a50e2",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "18cd6a16",
+   "id": "00eb27c4",
    "metadata": {},
    "source": [
     "#### 68. Considering a one-dimensional vector D, how to compute means of subsets of D using a vector S of same size describing subset  indices? (★★★)"
@@ -1162,14 +1162,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "2185257f",
+   "id": "d48c5210",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "fb2b3f5d",
+   "id": "928a1a15",
    "metadata": {},
    "source": [
     "#### 69. How to get the diagonal of a dot product? (★★★)"
@@ -1178,14 +1178,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "8ada08d1",
+   "id": "ef2c9ddd",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "3bb7807e",
+   "id": "5143f7f3",
    "metadata": {},
    "source": [
     "#### 70. Consider the vector [1, 2, 3, 4, 5], how to build a new vector with 3 consecutive zeros interleaved between each value? (★★★)"
@@ -1194,14 +1194,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "c173afdb",
+   "id": "1d99a1c1",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "40e4d74e",
+   "id": "f62551d8",
    "metadata": {},
    "source": [
     "#### 71. Consider an array of dimension (5,5,3), how to mulitply it by an array with dimensions (5,5)? (★★★)"
@@ -1210,14 +1210,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "32d15813",
+   "id": "9ab241b7",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "9ee9c5cc",
+   "id": "6896e326",
    "metadata": {},
    "source": [
     "#### 72. How to swap two rows of an array? (★★★)"
@@ -1226,14 +1226,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "8499665c",
+   "id": "9e8fcba9",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "2a16d4e2",
+   "id": "aeaf4a7b",
    "metadata": {},
    "source": [
     "#### 73. Consider a set of 10 triplets describing 10 triangles (with shared vertices), find the set of unique line segments composing all the  triangles (★★★)"
@@ -1242,14 +1242,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "4f2c6e17",
+   "id": "39ef4234",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "75bbcb12",
+   "id": "3d11451b",
    "metadata": {},
    "source": [
     "#### 74. Given a sorted array C that corresponds to a bincount, how to produce an array A such that np.bincount(A) == C? (★★★)"
@@ -1258,14 +1258,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "46ebf898",
+   "id": "a5563362",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "605b5b91",
+   "id": "a0a45995",
    "metadata": {},
    "source": [
     "#### 75. How to compute averages using a sliding window over an array? (★★★)"
@@ -1274,14 +1274,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "b6f28d8a",
+   "id": "116243d5",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "0a83c91b",
+   "id": "7808578f",
    "metadata": {},
    "source": [
     "#### 76. Consider a one-dimensional array Z, build a two-dimensional array whose first row is (Z[0],Z[1],Z[2]) and each subsequent row is  shifted by 1 (last row should be (Z[-3],Z[-2],Z[-1]) (★★★)"
@@ -1290,14 +1290,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "78b4cfb4",
+   "id": "6b23ba6e",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "4be00d5e",
+   "id": "8e83df46",
    "metadata": {},
    "source": [
     "#### 77. How to negate a boolean, or to change the sign of a float inplace? (★★★)"
@@ -1306,14 +1306,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "5ba94110",
+   "id": "f73127b7",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "23ff5523",
+   "id": "e67ff31c",
    "metadata": {},
    "source": [
     "#### 78. Consider 2 sets of points P0,P1 describing lines (2d) and a point p, how to compute distance from p to each line i (P0[i],P1[i])? (★★★)"
@@ -1322,14 +1322,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "4621c4e1",
+   "id": "89d75b76",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "bbba6526",
+   "id": "ad8821b1",
    "metadata": {},
    "source": [
     "#### 79. Consider 2 sets of points P0,P1 describing lines (2d) and a set of points P, how to compute distance from each point j (P[j]) to each line i (P0[i],P1[i])? (★★★)"
@@ -1338,14 +1338,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "a38de46e",
+   "id": "775feca0",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "b70a0169",
+   "id": "a0c8cbf5",
    "metadata": {},
    "source": [
     "#### 80. Consider an arbitrary array, write a function that extract a subpart with a fixed shape and centered on a given element (pad with a `fill` value when necessary) (★★★)"
@@ -1354,14 +1354,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "e286aa38",
+   "id": "381fd926",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "82577004",
+   "id": "781fa236",
    "metadata": {},
    "source": [
     "#### 81. Consider an array Z = [1,2,3,4,5,6,7,8,9,10,11,12,13,14], how to generate an array R = [[1,2,3,4], [2,3,4,5], [3,4,5,6], ..., [11,12,13,14]]? (★★★)"
@@ -1370,14 +1370,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "299febc3",
+   "id": "8e84d3c2",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "19914b7e",
+   "id": "9c9bb0f3",
    "metadata": {},
    "source": [
     "#### 82. Compute a matrix rank (★★★)"
@@ -1386,14 +1386,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "71b6d05e",
+   "id": "b75ef318",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "5b4702b1",
+   "id": "7d8dc135",
    "metadata": {},
    "source": [
     "#### 83. How to find the most frequent value in an array?"
@@ -1402,14 +1402,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "47392a08",
+   "id": "3978a7a2",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "e2b4e6d4",
+   "id": "aa340126",
    "metadata": {},
    "source": [
     "#### 84. Extract all the contiguous 3x3 blocks from a random 10x10 matrix (★★★)"
@@ -1418,14 +1418,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "ecc7884c",
+   "id": "bf138783",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "588931bf",
+   "id": "6b6d2c84",
    "metadata": {},
    "source": [
     "#### 85. Create a 2D array subclass such that Z[i,j] == Z[j,i] (★★★)"
@@ -1434,14 +1434,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "16415e97",
+   "id": "155e16ce",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "3e2ada58",
+   "id": "7be0fe36",
    "metadata": {},
    "source": [
     "#### 86. Consider a set of p matrices wich shape (n,n) and a set of p vectors with shape (n,1). How to compute the sum of of the p matrix products at once? (result has shape (n,1)) (★★★)"
@@ -1450,14 +1450,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "b830123b",
+   "id": "ea732c23",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "dc24b132",
+   "id": "a840a88f",
    "metadata": {},
    "source": [
     "#### 87. Consider a 16x16 array, how to get the block-sum (block size is 4x4)? (★★★)"
@@ -1466,14 +1466,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "2aecf16c",
+   "id": "6e0c1cbe",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "bc324c05",
+   "id": "c2bd7385",
    "metadata": {},
    "source": [
     "#### 88. How to implement the Game of Life using numpy arrays? (★★★)"
@@ -1482,14 +1482,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "fb2f76d6",
+   "id": "aea7d805",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "84266863",
+   "id": "4c70397b",
    "metadata": {},
    "source": [
     "#### 89. How to get the n largest values of an array (★★★)"
@@ -1498,14 +1498,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "3b353230",
+   "id": "16371718",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "4f5587b9",
+   "id": "15ba193c",
    "metadata": {},
    "source": [
     "#### 90. Given an arbitrary number of vectors, build the cartesian product (every combinations of every item) (★★★)"
@@ -1514,14 +1514,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "3f752a18",
+   "id": "c9c468d4",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "b4c22657",
+   "id": "ec828405",
    "metadata": {},
    "source": [
     "#### 91. How to create a record array from a regular array? (★★★)"
@@ -1530,14 +1530,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "a0dc0426",
+   "id": "84eb5fba",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "bb9f1473",
+   "id": "d94352b6",
    "metadata": {},
    "source": [
     "#### 92. Consider a large vector Z, compute Z to the power of 3 using 3 different methods (★★★)"
@@ -1546,14 +1546,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "0d585a57",
+   "id": "301ba8a8",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "3acb5b65",
+   "id": "7c3a9e32",
    "metadata": {},
    "source": [
     "#### 93. Consider two arrays A and B of shape (8,3) and (2,2). How to find rows of A that contain elements of each row of B regardless of the order of the elements in B? (★★★)"
@@ -1562,14 +1562,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "f9e1e127",
+   "id": "777376e3",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "f8f36be4",
+   "id": "da9d5eeb",
    "metadata": {},
    "source": [
     "#### 94. Considering a 10x3 matrix, extract rows with unequal values (e.g. [2,2,3]) (★★★)"
@@ -1578,14 +1578,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "6caa0f63",
+   "id": "67dbea5c",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "2065f6b5",
+   "id": "f7b65fd5",
    "metadata": {},
    "source": [
     "#### 95. Convert a vector of ints into a matrix binary representation (★★★)"
@@ -1594,14 +1594,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "8a6afb88",
+   "id": "127294ed",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "15953492",
+   "id": "2784c996",
    "metadata": {},
    "source": [
     "#### 96. Given a two dimensional array, how to extract unique rows? (★★★)"
@@ -1610,14 +1610,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "2fbe8159",
+   "id": "f030595f",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "95bce4fe",
+   "id": "71a7574c",
    "metadata": {},
    "source": [
     "#### 97. Considering 2 vectors A & B, write the einsum equivalent of inner, outer, sum, and mul function (★★★)"
@@ -1626,14 +1626,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "07971442",
+   "id": "721c4e1a",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "6d728760",
+   "id": "30f06441",
    "metadata": {},
    "source": [
     "#### 98. Considering a path described by two vectors (X,Y), how to sample it using equidistant samples (★★★)?"
@@ -1642,14 +1642,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "2a30f221",
+   "id": "fb41c022",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "5b3bbdc0",
+   "id": "e5737276",
    "metadata": {},
    "source": [
     "#### 99. Given an integer n and a 2D array X, select from X the rows which can be interpreted as draws from a multinomial distribution with n degrees, i.e., the rows which only contain integers and which sum to n. (★★★)"
@@ -1658,14 +1658,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "eb9bad02",
+   "id": "68c333b0",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "6295db88",
+   "id": "5882e36d",
    "metadata": {},
    "source": [
     "#### 100. Compute bootstrapped 95% confidence intervals for the mean of a 1D array X (i.e., resample the elements of an array with replacement N times, compute the mean of each sample, and then compute percentiles over the means). (★★★)"
@@ -1674,7 +1674,7 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "94174a6b",
+   "id": "d1b566e5",
    "metadata": {},
    "outputs": [],
    "source": []
diff --git a/100_Numpy_exercises.md b/100_Numpy_exercises.md
index 3319bc0..edeee60 100644
--- a/100_Numpy_exercises.md
+++ b/100_Numpy_exercises.md
@@ -58,7 +58,7 @@ np.nan in set([np.nan])
 
 #### 19. Create a 8x8 matrix and fill it with a checkerboard pattern (★☆☆)
 
-#### 20. Consider a (6,7,8) shape array, what is the index (x,y,z) of the 100th element?
+#### 20. Consider a (6,7,8) shape array, what is the index (x,y,z) of the 100th element? (★☆☆)
 
 #### 21. Create a checkerboard 8x8 matrix using the tile function (★☆☆)
 
@@ -89,7 +89,7 @@ Z/1/1
 Z<Z>Z
 ```
 
-#### 28. What are the result of the following expressions?
+#### 28. What are the result of the following expressions? (★☆☆)
 ```python
 np.array(0) / np.array(0)
 np.array(0) // np.array(0)
@@ -135,7 +135,7 @@ np.sqrt(-1) == np.emath.sqrt(-1)
 
 #### 46. Create a structured array with `x` and `y` coordinates covering the [0,1]x[0,1] area (★★☆)
 
-#### 47. Given two arrays, X and Y, construct the Cauchy matrix C (Cij =1/(xi - yj))
+#### 47. Given two arrays, X and Y, construct the Cauchy matrix C (Cij =1/(xi - yj)) (★★☆)
 
 #### 48. Print the minimum and maximum representable value for each numpy scalar type (★★☆)
 
diff --git a/100_Numpy_exercises_with_hints.md b/100_Numpy_exercises_with_hints.md
index 74c1bca..5b8db89 100644
--- a/100_Numpy_exercises_with_hints.md
+++ b/100_Numpy_exercises_with_hints.md
@@ -58,7 +58,7 @@ np.nan in set([np.nan])
 `hint: np.diag`
 #### 19. Create a 8x8 matrix and fill it with a checkerboard pattern (★☆☆)
 `hint: array[::2]`
-#### 20. Consider a (6,7,8) shape array, what is the index (x,y,z) of the 100th element?
+#### 20. Consider a (6,7,8) shape array, what is the index (x,y,z) of the 100th element? (★☆☆)
 `hint: np.unravel_index`
 #### 21. Create a checkerboard 8x8 matrix using the tile function (★☆☆)
 `hint: np.tile`
@@ -89,7 +89,7 @@ Z/1/1
 Z<Z>Z
 ```
 `No hints provided...`
-#### 28. What are the result of the following expressions?
+#### 28. What are the result of the following expressions? (★☆☆)
 ```python
 np.array(0) / np.array(0)
 np.array(0) // np.array(0)
@@ -135,7 +135,7 @@ np.sqrt(-1) == np.emath.sqrt(-1)
 `hint: argmax`
 #### 46. Create a structured array with `x` and `y` coordinates covering the [0,1]x[0,1] area (★★☆)
 `hint: np.meshgrid`
-#### 47. Given two arrays, X and Y, construct the Cauchy matrix C (Cij =1/(xi - yj))
+#### 47. Given two arrays, X and Y, construct the Cauchy matrix C (Cij =1/(xi - yj)) (★★☆)
 `hint: np.subtract.outer`
 #### 48. Print the minimum and maximum representable value for each numpy scalar type (★★☆)
 `hint: np.iinfo, np.finfo, eps`
diff --git a/100_Numpy_exercises_with_hints_with_solutions.md b/100_Numpy_exercises_with_hints_with_solutions.md
index e346bb3..f8b3f3d 100644
--- a/100_Numpy_exercises_with_hints_with_solutions.md
+++ b/100_Numpy_exercises_with_hints_with_solutions.md
@@ -168,7 +168,7 @@ Z[1::2,::2] = 1
 Z[::2,1::2] = 1
 print(Z)
 ```
-#### 20. Consider a (6,7,8) shape array, what is the index (x,y,z) of the 100th element?
+#### 20. Consider a (6,7,8) shape array, what is the index (x,y,z) of the 100th element? (★☆☆)
 `hint: np.unravel_index`
 
 ```python
@@ -255,7 +255,7 @@ Z <- Z
 Z/1/1
 Z<Z>Z
 ```
-#### 28. What are the result of the following expressions?
+#### 28. What are the result of the following expressions? (★☆☆)
 ```python
 np.array(0) / np.array(0)
 np.array(0) // np.array(0)
@@ -447,7 +447,7 @@ Z['x'], Z['y'] = np.meshgrid(np.linspace(0,1,5),
                              np.linspace(0,1,5))
 print(Z)
 ```
-#### 47. Given two arrays, X and Y, construct the Cauchy matrix C (Cij =1/(xi - yj))
+#### 47. Given two arrays, X and Y, construct the Cauchy matrix C (Cij =1/(xi - yj)) (★★☆)
 `hint: np.subtract.outer`
 
 ```python
@@ -827,7 +827,7 @@ from numpy.lib import stride_tricks
 
 def rolling(a, window):
     shape = (a.size - window + 1, window)
-    strides = (a.itemsize, a.itemsize)
+    strides = (a.strides[0], a.strides[0])
     return stride_tricks.as_strided(a, shape=shape, strides=strides)
 Z = rolling(np.arange(10), 3)
 print(Z)
diff --git a/100_Numpy_exercises_with_solutions.md b/100_Numpy_exercises_with_solutions.md
index da812a9..99fea53 100644
--- a/100_Numpy_exercises_with_solutions.md
+++ b/100_Numpy_exercises_with_solutions.md
@@ -168,7 +168,7 @@ Z[1::2,::2] = 1
 Z[::2,1::2] = 1
 print(Z)
 ```
-#### 20. Consider a (6,7,8) shape array, what is the index (x,y,z) of the 100th element?
+#### 20. Consider a (6,7,8) shape array, what is the index (x,y,z) of the 100th element? (★☆☆)
 
 
 ```python
@@ -255,7 +255,7 @@ Z <- Z
 Z/1/1
 Z<Z>Z
 ```
-#### 28. What are the result of the following expressions?
+#### 28. What are the result of the following expressions? (★☆☆)
 ```python
 np.array(0) / np.array(0)
 np.array(0) // np.array(0)
@@ -447,7 +447,7 @@ Z['x'], Z['y'] = np.meshgrid(np.linspace(0,1,5),
                              np.linspace(0,1,5))
 print(Z)
 ```
-#### 47. Given two arrays, X and Y, construct the Cauchy matrix C (Cij =1/(xi - yj))
+#### 47. Given two arrays, X and Y, construct the Cauchy matrix C (Cij =1/(xi - yj)) (★★☆)
 
 
 ```python
@@ -827,7 +827,7 @@ from numpy.lib import stride_tricks
 
 def rolling(a, window):
     shape = (a.size - window + 1, window)
-    strides = (a.itemsize, a.itemsize)
+    strides = (a.strides[0], a.strides[0])
     return stride_tricks.as_strided(a, shape=shape, strides=strides)
 Z = rolling(np.arange(10), 3)
 print(Z)
diff --git a/100_Numpy_random.ipynb b/100_Numpy_random.ipynb
index 41904f8..704e34e 100644
--- a/100_Numpy_random.ipynb
+++ b/100_Numpy_random.ipynb
@@ -2,7 +2,7 @@
  "cells": [
   {
    "cell_type": "markdown",
-   "id": "9187d1fe",
+   "id": "bbe15f43",
    "metadata": {},
    "source": [
     "# 100 numpy exercises\n",
@@ -18,7 +18,7 @@
   },
   {
    "cell_type": "markdown",
-   "id": "7b3fced0",
+   "id": "ed56e5f0",
    "metadata": {},
    "source": [
     "File automatically generated. See the documentation to update questions/answers/hints programmatically."
@@ -26,7 +26,7 @@
   },
   {
    "cell_type": "markdown",
-   "id": "77575766",
+   "id": "14866554",
    "metadata": {},
    "source": [
     "Run the `initialize.py` module, then call a random question with `pick()` an hint towards its solution with\n",
@@ -36,7 +36,7 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "bcf0dd93",
+   "id": "af8b6f2a",
    "metadata": {},
    "outputs": [],
    "source": [
@@ -46,7 +46,7 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "f401c090",
+   "id": "f13ecfd7",
    "metadata": {},
    "outputs": [],
    "source": [
diff --git a/source/exercises100.ktx b/source/exercises100.ktx
index 5d2aea9..aaa394e 100644
--- a/source/exercises100.ktx
+++ b/source/exercises100.ktx
@@ -212,7 +212,7 @@ Z[::2,1::2] = 1
 print(Z)
 
 < q20
-Consider a (6,7,8) shape array, what is the index (x,y,z) of the 100th element?
+Consider a (6,7,8) shape array, what is the index (x,y,z) of the 100th element? (★☆☆)
 
 < h20
 hint: np.unravel_index
@@ -323,7 +323,7 @@ Z/1/1
 Z<Z>Z
 
 < q28
-What are the result of the following expressions?
+What are the result of the following expressions? (★☆☆)
 ```python
 np.array(0) / np.array(0)
 np.array(0) // np.array(0)
@@ -572,7 +572,7 @@ Z['x'], Z['y'] = np.meshgrid(np.linspace(0,1,5),
 print(Z)
 
 < q47
-Given two arrays, X and Y, construct the Cauchy matrix C (Cij =1/(xi - yj))
+Given two arrays, X and Y, construct the Cauchy matrix C (Cij =1/(xi - yj)) (★★☆)
 
 < h47
 hint: np.subtract.outer