diff --git a/100_Numpy_exercises.ipynb b/100_Numpy_exercises.ipynb
index 39b8d97..a1590c3 100644
--- a/100_Numpy_exercises.ipynb
+++ b/100_Numpy_exercises.ipynb
@@ -2,7 +2,7 @@
  "cells": [
   {
    "cell_type": "markdown",
-   "id": "24963653",
+   "id": "9a9aa121",
    "metadata": {},
    "source": [
     "# 100 numpy exercises\n",
@@ -18,7 +18,7 @@
   },
   {
    "cell_type": "markdown",
-   "id": "59ddae7e",
+   "id": "8befc7ce",
    "metadata": {},
    "source": [
     "File automatically generated. See the documentation to update questions/answers/hints programmatically."
@@ -26,7 +26,7 @@
   },
   {
    "cell_type": "markdown",
-   "id": "4a02b98c",
+   "id": "6f825f1c",
    "metadata": {},
    "source": [
     "Run the `initialise.py` module, then for each question you can query the\n",
@@ -36,7 +36,7 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "c2161124",
+   "id": "703184e0",
    "metadata": {},
    "outputs": [],
    "source": [
@@ -45,7 +45,7 @@
   },
   {
    "cell_type": "markdown",
-   "id": "96fe6659",
+   "id": "d1f04fa5",
    "metadata": {},
    "source": [
     "#### 1. Import the numpy package under the name `np` (★☆☆)"
@@ -54,14 +54,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "9ffea9a1",
+   "id": "bc171159",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "126932fd",
+   "id": "4fb231dc",
    "metadata": {},
    "source": [
     "#### 2. Print the numpy version and the configuration (★☆☆)"
@@ -70,14 +70,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "fdd0d7a8",
+   "id": "b2ed5c7c",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "43c84f29",
+   "id": "04caf5c7",
    "metadata": {},
    "source": [
     "#### 3. Create a null vector of size 10 (★☆☆)"
@@ -86,14 +86,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "e007a9d1",
+   "id": "42e74a30",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "22dc97de",
+   "id": "751cf42e",
    "metadata": {},
    "source": [
     "#### 4. How to find the memory size of any array (★☆☆)"
@@ -102,14 +102,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "d27dba65",
+   "id": "97c5fbab",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "4e5bae8d",
+   "id": "88a97f0c",
    "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": "1dbbbed8",
+   "id": "92abb854",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "fcfdbff1",
+   "id": "a7671961",
    "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": "0387a362",
+   "id": "6c38f791",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "bdf2ba90",
+   "id": "8e5fdd72",
    "metadata": {},
    "source": [
     "#### 7. Create a vector with values ranging from 10 to 49 (★☆☆)"
@@ -150,14 +150,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "81f0a925",
+   "id": "0c911e4b",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "5d0c6cfe",
+   "id": "de9853d4",
    "metadata": {},
    "source": [
     "#### 8. Reverse a vector (first element becomes last) (★☆☆)"
@@ -166,14 +166,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "8e7754ae",
+   "id": "63ec0dea",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "3f5bef92",
+   "id": "a35c1207",
    "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": "e0e277fc",
+   "id": "bde1723f",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "14b44c2e",
+   "id": "9ad0f11f",
    "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": "1ad14e21",
+   "id": "959823d4",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "67c0f072",
+   "id": "d3c8eac1",
    "metadata": {},
    "source": [
     "#### 11. Create a 3x3 identity matrix (★☆☆)"
@@ -214,14 +214,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "ca2bc573",
+   "id": "306a48be",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "097460e8",
+   "id": "a905079b",
    "metadata": {},
    "source": [
     "#### 12. Create a 3x3x3 array with random values (★☆☆)"
@@ -230,14 +230,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "4bd63c1f",
+   "id": "3bd26f5d",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "f7a72443",
+   "id": "cbf5cf4a",
    "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": "86d85900",
+   "id": "a0686c44",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "2100731f",
+   "id": "b322aab7",
    "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": "63e2bbf2",
+   "id": "97dce1ea",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "dfb30185",
+   "id": "101e9f4f",
    "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": "480afa6b",
+   "id": "55b6af0c",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "36e4de87",
+   "id": "b75a05e9",
    "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": "5ac52150",
+   "id": "771b07f2",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "6f43f816",
+   "id": "d773a68e",
    "metadata": {},
    "source": [
     "#### 17. What is the result of the following expression? (★☆☆)\n",
@@ -318,14 +318,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "f2395fda",
+   "id": "5283493c",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "446f87e0",
+   "id": "569089c1",
    "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": "58d0e495",
+   "id": "acdd4875",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "b6366cdb",
+   "id": "c757729e",
    "metadata": {},
    "source": [
     "#### 19. Create a 8x8 matrix and fill it with a checkerboard pattern (★☆☆)"
@@ -350,14 +350,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "54d459ce",
+   "id": "a96e0ca1",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "35077361",
+   "id": "63d93126",
    "metadata": {},
    "source": [
     "#### 20. Consider a (6,7,8) shape array, what is the index (x,y,z) of the 100th element? (★☆☆)"
@@ -366,14 +366,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "d9cbcf85",
+   "id": "22800ac9",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "ef02a06b",
+   "id": "237998f6",
    "metadata": {},
    "source": [
     "#### 21. Create a checkerboard 8x8 matrix using the tile function (★☆☆)"
@@ -382,14 +382,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "a29c4af1",
+   "id": "22a86261",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "4fc8f909",
+   "id": "578e1eca",
    "metadata": {},
    "source": [
     "#### 22. Normalize a 5x5 random matrix (★☆☆)"
@@ -398,14 +398,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "ddb836b9",
+   "id": "b07707b1",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "b2083fc7",
+   "id": "57d1fff2",
    "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": "28bd9e0b",
+   "id": "1ea1a438",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "8bfb605c",
+   "id": "08189760",
    "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": "0e4525f6",
+   "id": "2b120295",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "d945b917",
+   "id": "3fa7d315",
    "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": "13ea9d0c",
+   "id": "52e10a95",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "80e3937d",
+   "id": "6100c656",
    "metadata": {},
    "source": [
     "#### 26. What is the output of the following script? (★☆☆)\n",
@@ -469,14 +469,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "3268939a",
+   "id": "099d3b5f",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "4e586977",
+   "id": "21cadfdb",
    "metadata": {},
    "source": [
     "#### 27. Consider an integer vector Z, which of these expressions are legal? (★☆☆)\n",
@@ -493,14 +493,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "1f36c9d4",
+   "id": "eefdc61f",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "4db5a6d5",
+   "id": "edb05d8c",
    "metadata": {},
    "source": [
     "#### 28. What are the result of the following expressions? (★☆☆)\n",
@@ -514,14 +514,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "a38701d1",
+   "id": "98cf2ccd",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "b4d3080a",
+   "id": "e125e143",
    "metadata": {},
    "source": [
     "#### 29. How to round away from zero a float array ? (★☆☆)"
@@ -530,14 +530,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "84c7b39e",
+   "id": "ac635a3c",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "4f89952c",
+   "id": "6fbcfde4",
    "metadata": {},
    "source": [
     "#### 30. How to find common values between two arrays? (★☆☆)"
@@ -546,14 +546,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "ec4561c9",
+   "id": "cef72c3d",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "26bf6974",
+   "id": "448290f7",
    "metadata": {},
    "source": [
     "#### 31. How to ignore all numpy warnings (not recommended)? (★☆☆)"
@@ -562,14 +562,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "950d597f",
+   "id": "570ffcdb",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "261fd76b",
+   "id": "a9634713",
    "metadata": {},
    "source": [
     "#### 32. Is the following expressions true? (★☆☆)\n",
@@ -581,14 +581,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "96eb8b24",
+   "id": "ea730787",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "4a82256f",
+   "id": "ca2c7bd0",
    "metadata": {},
    "source": [
     "#### 33. How to get the dates of yesterday, today and tomorrow? (★☆☆)"
@@ -597,14 +597,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "4cff80dd",
+   "id": "e771971c",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "d90599b6",
+   "id": "2ad51e8b",
    "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": "16337844",
+   "id": "265753fd",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "aa35839c",
+   "id": "a58b5c61",
    "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": "54b8178b",
+   "id": "2a29953f",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "13bc061a",
+   "id": "76f22ae3",
    "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": "c8fee789",
+   "id": "0990421d",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "f01b9650",
+   "id": "994a8b81",
    "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": "ab1101be",
+   "id": "3cbaa01b",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "35976e4b",
+   "id": "c7d368b0",
    "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": "7ca66207",
+   "id": "92c49778",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "edb9a160",
+   "id": "6adeb79d",
    "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": "67aaf30a",
+   "id": "21e51b0f",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "69a3604b",
+   "id": "1cdc3d67",
    "metadata": {},
    "source": [
     "#### 40. Create a random vector of size 10 and sort it (★★☆)"
@@ -709,14 +709,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "278e79e3",
+   "id": "24d950b4",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "05ec5273",
+   "id": "a2da25e2",
    "metadata": {},
    "source": [
     "#### 41. How to sum a small array faster than np.sum? (★★☆)"
@@ -725,14 +725,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "94eea81d",
+   "id": "d7ca546d",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "d310ff7e",
+   "id": "19cc3ede",
    "metadata": {},
    "source": [
     "#### 42. Consider two random arrays A and B, check if they are equal (★★☆)"
@@ -741,14 +741,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "754e9de5",
+   "id": "5c055834",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "dab5009d",
+   "id": "7df700bc",
    "metadata": {},
    "source": [
     "#### 43. Make an array immutable (read-only) (★★☆)"
@@ -757,14 +757,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "496ac553",
+   "id": "a5f059a0",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "71643a79",
+   "id": "982e2f7e",
    "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": "60d87877",
+   "id": "d9423986",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "8ed31762",
+   "id": "b5863c52",
    "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": "6097ec5e",
+   "id": "3b65f66f",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "1a0d5a6b",
+   "id": "2a12f2ae",
    "metadata": {},
    "source": [
     "#### 46. Create a structured array with `x` and `y` coordinates covering the [0,1]x[0,1] area (★★☆)"
@@ -805,14 +805,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "749e196f",
+   "id": "65763e44",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "ebc0da7d",
+   "id": "9be0eb72",
    "metadata": {},
    "source": [
     "#### 47. Given two arrays, X and Y, construct the Cauchy matrix C (Cij =1/(xi - yj)) (★★☆)"
@@ -821,14 +821,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "eb21da87",
+   "id": "d999c9c6",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "8f3327cb",
+   "id": "864fda69",
    "metadata": {},
    "source": [
     "#### 48. Print the minimum and maximum representable values for each numpy scalar type (★★☆)"
@@ -837,14 +837,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "3f197c5a",
+   "id": "03e5dc9e",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "207e37c6",
+   "id": "e6437089",
    "metadata": {},
    "source": [
     "#### 49. How to print all the values of an array? (★★☆)"
@@ -853,14 +853,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "b9165f3d",
+   "id": "d0b8972b",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "1bda9a9a",
+   "id": "59b3f402",
    "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": "86771556",
+   "id": "9c3702bb",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "0f057548",
+   "id": "5161a0e8",
    "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": "b71873c2",
+   "id": "fee3d794",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "47118bd1",
+   "id": "f0c0a11e",
    "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": "567883c7",
+   "id": "6fdb2124",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "21d6ebad",
+   "id": "13007015",
    "metadata": {},
    "source": [
     "#### 53. How to convert a float (32 bits) array into an integer (32 bits) array in place?"
@@ -917,14 +917,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "c27bac6f",
+   "id": "6b691b3b",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "0c71ff26",
+   "id": "3acba415",
    "metadata": {},
    "source": [
     "#### 54. How to read the following file? (★★☆)\n",
@@ -938,14 +938,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "efdf3972",
+   "id": "8505835e",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "5953f719",
+   "id": "0c46d792",
    "metadata": {},
    "source": [
     "#### 55. What is the equivalent of enumerate for numpy arrays? (★★☆)"
@@ -954,14 +954,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "d7e34455",
+   "id": "85fdeb4a",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "87ded306",
+   "id": "9e276331",
    "metadata": {},
    "source": [
     "#### 56. Generate a generic 2D Gaussian-like array (★★☆)"
@@ -970,14 +970,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "171a6cbc",
+   "id": "5f1d784a",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "fcfd2f70",
+   "id": "da594a47",
    "metadata": {},
    "source": [
     "#### 57. How to randomly place p elements in a 2D array? (★★☆)"
@@ -986,14 +986,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "1804e4ab",
+   "id": "b4f5aedd",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "f0b9b18b",
+   "id": "5a8e20eb",
    "metadata": {},
    "source": [
     "#### 58. Subtract the mean of each row of a matrix (★★☆)"
@@ -1002,14 +1002,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "eac4c892",
+   "id": "0850bec6",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "61e40ad7",
+   "id": "529d3c17",
    "metadata": {},
    "source": [
     "#### 59. How to sort an array by the nth column? (★★☆)"
@@ -1018,14 +1018,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "c687d9f1",
+   "id": "0d401082",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "9a4f7fb1",
+   "id": "0f6680ae",
    "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": "021aa204",
+   "id": "fe60a4d0",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "bff8d09f",
+   "id": "f33c3a84",
    "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": "a340d3dc",
+   "id": "d45b9371",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "033f7e4e",
+   "id": "c2f889ed",
    "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": "f7bc41aa",
+   "id": "57ea3125",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "8035a7b7",
+   "id": "dcb09dcd",
    "metadata": {},
    "source": [
     "#### 63. Create an array class that has a name attribute (★★☆)"
@@ -1082,14 +1082,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "0f19321f",
+   "id": "d7bd3904",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "fa4dbf31",
+   "id": "b0e91553",
    "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": "85893b93",
+   "id": "3affc760",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "d55ea9ef",
+   "id": "e0385252",
    "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": "7241b03f",
+   "id": "c9e111a0",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "3d5ad91f",
+   "id": "30ceeeb5",
    "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": "2f8d8c18",
+   "id": "a07bac48",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "e4c0ca46",
+   "id": "f2c4f7fe",
    "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": "cb30cb50",
+   "id": "377e2aa2",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "68781ae8",
+   "id": "0748b433",
    "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": "a1a09f76",
+   "id": "458ead5a",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "42ec30c3",
+   "id": "fca120bf",
    "metadata": {},
    "source": [
     "#### 69. How to get the diagonal of a dot product? (★★★)"
@@ -1178,14 +1178,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "77008bcb",
+   "id": "aabe682a",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "72cd1881",
+   "id": "a53781d5",
    "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": "d237d266",
+   "id": "f596a9f0",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "00e60dbf",
+   "id": "8d4c4bcc",
    "metadata": {},
    "source": [
     "#### 71. Consider an array of dimension (5,5,3), how to multiply it by an array with dimensions (5,5)? (★★★)"
@@ -1210,14 +1210,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "55f0e1d4",
+   "id": "7eb126d1",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "0ba31fcd",
+   "id": "870c6b3e",
    "metadata": {},
    "source": [
     "#### 72. How to swap two rows of an array? (★★★)"
@@ -1226,14 +1226,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "9fd8d80e",
+   "id": "018a1fce",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "84f66062",
+   "id": "f807b95a",
    "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": "3d92aac2",
+   "id": "182d7ab8",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "18c7d944",
+   "id": "127d6162",
    "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": "1f82e01e",
+   "id": "58bfa175",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "de0fbc43",
+   "id": "bea3a91d",
    "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": "7d6d173f",
+   "id": "3da93cb6",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "3caf673b",
+   "id": "71481034",
    "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": "1b51c8bc",
+   "id": "b1419349",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "55ae7213",
+   "id": "29041930",
    "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": "f09474c7",
+   "id": "0f8c2129",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "453aed20",
+   "id": "75fd8ebf",
    "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": "288111ad",
+   "id": "e08558dc",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "a2242b1e",
+   "id": "1248ffc8",
    "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": "1238f08b",
+   "id": "53f1708e",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "07c63697",
+   "id": "76875c5a",
    "metadata": {},
    "source": [
     "#### 80. Consider an arbitrary array, write a function that extracts 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": "01e418e9",
+   "id": "165687fa",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "8f46a3e6",
+   "id": "cdaf9927",
    "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": "645a43d1",
+   "id": "f2312a8b",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "339d1830",
+   "id": "f60ed7e8",
    "metadata": {},
    "source": [
     "#### 82. Compute a matrix rank (★★★)"
@@ -1386,14 +1386,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "55909d61",
+   "id": "53d7964b",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "94599b6d",
+   "id": "9df16ebf",
    "metadata": {},
    "source": [
     "#### 83. How to find the most frequent value in an array?"
@@ -1402,14 +1402,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "cb701ed6",
+   "id": "b4ee330e",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "3f2ff8f2",
+   "id": "730664dc",
    "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": "93e6f167",
+   "id": "a828d6f9",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "f70e04be",
+   "id": "8734d0ef",
    "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": "795e513d",
+   "id": "35f465a1",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "08da7b7a",
+   "id": "bb4493e6",
    "metadata": {},
    "source": [
     "#### 86. Consider a set of p matrices with 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": "9890ed56",
+   "id": "5f3d2af1",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "7853fe1e",
+   "id": "c4da8597",
    "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": "146e3ada",
+   "id": "f6ea8bcd",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "2421dc6d",
+   "id": "c0fab898",
    "metadata": {},
    "source": [
     "#### 88. How to implement the Game of Life using numpy arrays? (★★★)"
@@ -1482,14 +1482,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "06ade5e0",
+   "id": "7265ae17",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "57aee892",
+   "id": "376e5084",
    "metadata": {},
    "source": [
     "#### 89. How to get the n largest values of an array (★★★)"
@@ -1498,14 +1498,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "29d72cd2",
+   "id": "4141f5ab",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "0e2da2b5",
+   "id": "391538a7",
    "metadata": {},
    "source": [
     "#### 90. Given an arbitrary number of vectors, build the cartesian product (every combination of every item) (★★★)"
@@ -1514,14 +1514,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "54874b32",
+   "id": "2d969dbe",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "2ed5c735",
+   "id": "53187ef3",
    "metadata": {},
    "source": [
     "#### 91. How to create a record array from a regular array? (★★★)"
@@ -1530,14 +1530,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "4e826b8c",
+   "id": "44ae3756",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "d91cfe01",
+   "id": "6702714f",
    "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": "b610d5b1",
+   "id": "5fd2ce21",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "29645461",
+   "id": "4a093a17",
    "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": "9b8ceb78",
+   "id": "c51bb071",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "687c2370",
+   "id": "78e0b17f",
    "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": "8455c06b",
+   "id": "aa3b5e56",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "3726eeed",
+   "id": "531cf623",
    "metadata": {},
    "source": [
     "#### 95. Convert a vector of ints into a matrix binary representation (★★★)"
@@ -1594,14 +1594,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "cc0652d4",
+   "id": "140abfed",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "d31a4ffd",
+   "id": "c7e0f77f",
    "metadata": {},
    "source": [
     "#### 96. Given a two dimensional array, how to extract unique rows? (★★★)"
@@ -1610,14 +1610,14 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "7a31971b",
+   "id": "b3add5bb",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "8b798880",
+   "id": "f85e3d17",
    "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": "c8d2fc50",
+   "id": "5d8603d7",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "07655168",
+   "id": "f1bae5a9",
    "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": "75b400ec",
+   "id": "5e40ac5c",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "d9f463ce",
+   "id": "ef87eba2",
    "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": "229d9f12",
+   "id": "e8de02d6",
    "metadata": {},
    "outputs": [],
    "source": []
   },
   {
    "cell_type": "markdown",
-   "id": "b019af39",
+   "id": "e2b693f7",
    "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": "b86a6fce",
+   "id": "cd36404a",
    "metadata": {},
    "outputs": [],
    "source": []
diff --git a/100_Numpy_exercises_with_hints_with_solutions.md b/100_Numpy_exercises_with_hints_with_solutions.md
index b028ed2..15c40cb 100644
--- a/100_Numpy_exercises_with_hints_with_solutions.md
+++ b/100_Numpy_exercises_with_hints_with_solutions.md
@@ -565,10 +565,18 @@ for index in np.ndindex(Z.shape):
 `hint: np.meshgrid, np.exp`
 
 ```python
-X, Y = np.meshgrid(np.linspace(-1,1,10), np.linspace(-1,1,10))
-D = np.sqrt(X*X+Y*Y)
+X, Y = np.meshgrid(np.linspace(-1, 1, 10), np.linspace(-1, 1, 10))
 sigma, mu = 1.0, 0.0
-G = np.exp(-( (D-mu)**2 / ( 2.0 * sigma**2 ) ) )
+G = np.exp(-((X - mu) ** 2 + (Y - mu) ** 2) / (2.0 * sigma**2))
+print(G)
+
+# Another solution using the fact that a 2D Gaussian is separable
+# Author: Nin17
+x = np.linspace(-1, 1, 10)
+y = np.linspace(-1, 1, 10)
+gx = np.exp(-((x - mu) ** 2 / (2.0 * sigma**2)))
+gy = np.exp(-((y - mu) ** 2 / (2.0 * sigma**2)))
+G = gy[:, None] * gx[None, :]
 print(G)
 ```
 #### 57. How to randomly place p elements in a 2D array? (★★☆)
diff --git a/100_Numpy_exercises_with_solutions.md b/100_Numpy_exercises_with_solutions.md
index 13ed8dd..1032820 100644
--- a/100_Numpy_exercises_with_solutions.md
+++ b/100_Numpy_exercises_with_solutions.md
@@ -565,10 +565,18 @@ for index in np.ndindex(Z.shape):
 
 
 ```python
-X, Y = np.meshgrid(np.linspace(-1,1,10), np.linspace(-1,1,10))
-D = np.sqrt(X*X+Y*Y)
+X, Y = np.meshgrid(np.linspace(-1, 1, 10), np.linspace(-1, 1, 10))
 sigma, mu = 1.0, 0.0
-G = np.exp(-( (D-mu)**2 / ( 2.0 * sigma**2 ) ) )
+G = np.exp(-((X - mu) ** 2 + (Y - mu) ** 2) / (2.0 * sigma**2))
+print(G)
+
+# Another solution using the fact that a 2D Gaussian is separable
+# Author: Nin17
+x = np.linspace(-1, 1, 10)
+y = np.linspace(-1, 1, 10)
+gx = np.exp(-((x - mu) ** 2 / (2.0 * sigma**2)))
+gy = np.exp(-((y - mu) ** 2 / (2.0 * sigma**2)))
+G = gy[:, None] * gx[None, :]
 print(G)
 ```
 #### 57. How to randomly place p elements in a 2D array? (★★☆)
diff --git a/100_Numpy_random.ipynb b/100_Numpy_random.ipynb
index dd8253d..f80bcf4 100644
--- a/100_Numpy_random.ipynb
+++ b/100_Numpy_random.ipynb
@@ -2,7 +2,7 @@
  "cells": [
   {
    "cell_type": "markdown",
-   "id": "a3747e86",
+   "id": "94b10be0",
    "metadata": {},
    "source": [
     "# 100 numpy exercises\n",
@@ -18,7 +18,7 @@
   },
   {
    "cell_type": "markdown",
-   "id": "8b9ef9a4",
+   "id": "1d0b9900",
    "metadata": {},
    "source": [
     "File automatically generated. See the documentation to update questions/answers/hints programmatically."
@@ -26,7 +26,7 @@
   },
   {
    "cell_type": "markdown",
-   "id": "792c1217",
+   "id": "21313ae9",
    "metadata": {},
    "source": [
     "Run the `initialise.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": "541f746c",
+   "id": "c4ad3a14",
    "metadata": {},
    "outputs": [],
    "source": [
@@ -46,7 +46,7 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "id": "d1743adb",
+   "id": "13bdf6d0",
    "metadata": {},
    "outputs": [],
    "source": [