NOTE: this website is out of date. This is the course web site from a past quarter. If you are a current student taking the course, you should visit the current class web site instead. If the current website is not yet visible by going to cs107.stanford.edu, it may be accessible by visiting this link until the new page is mounted at this address. Please be advised that courses' policies change with each new quarter and instructor, and any information on this out-of-date page may not apply to you.
Written by Julie Zelenski
This puzzle is reproduced from a cereal box. Thanks to CS Lecturer Nick Parlante for this trick!
Get our your scissors and prepare to win yourself a few bets with this trick. Cut out the cards below. Have a volunteer pick a number between 1 and 63, hand these cards to them, and ask them to give you back only those cards on which their chosen number appears. In a feat of amazing wizardry, you then immediately tell them what their number is. How do the cards work?
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51 53 55 57 59 61 63 |
2 3 6 7 10 11 14 15 18 19 22 23 26 27 30 31 34 35 38 39 42 43 46 47 50 51 54 55 58 59 62 63 |
4 5 6 7 12 13 14 15 20 21 22 23 28 29 30 31 36 37 38 39 44 45 46 47 52 53 54 55 60 61 62 63 |
8 9 10 11 12 13 14 15 24 25 26 27 28 29 30 31 40 41 42 43 44 45 46 47 56 57 58 59 60 61 62 63 |
16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 |
32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 |