{ "metadata": { "name": "", "signature": "sha256:b9e2e6c3f7e82432833f1416dd0552c13753f683e1888682faf2910ef7d9f8ff" }, "nbformat": 3, "nbformat_minor": 0, "worksheets": [ { "cells": [ { "cell_type": "markdown", "metadata": {}, "source": [ "When is Cheryl's Birthday?\n", "===\n", "\n", "
Peter Norvig, April 2015
\n", "\n", "This logic puzzle has been [making the rounds](https://www.google.com/webhp?#q=cheryl%27s+birthday):\n", "\n", "\n", "1. Albert and Bernard just became friends with Cheryl, and they want to know when her birtxhday is. Cheryl gave them a list of 10 possible dates:\n", "
```\n",
"       May 15     May 16     May 19\n",
"      June 17    June 18\n",
"      July 14    July 16\n",
"    August 14  August 15  August 17\n",
"```
\n", " \n", "2. Cheryl then tells Albert and Bernard separately the month and the day of the birthday respectively.\n", " \n", "3. **Albert**: I don't know when Cheryl's birthday is, but I know that Bernard does not know too.\n", " \n", "4. **Bernard**: At first I don't know when Cheryl's birthday is, but I know now.\n", " \n", "5. **Albert**: Then I also know when Cheryl's birthday is.\n", " \n", "6. So when is Cheryl's birthday?