While your co-geeks may out this as a simple math trick, most people unable to recite pi past the decimal point will be amazed. It also has the advantage of requiring almost no physical, sleight-of-hand expertise.

1. Set the deck—from the top down, it should read 2, 3, 4, 5, 6, 7, 8, 9, A, A, A, A (the numbers in any suit and all four aces).

2. Shuffle, being sure not to affect the top 12 cards (yes, this is a cheap trick).

3. Ask an audience member to pick and state a number between 10 and 20 (not 20!).

4. Taking one at a time from the top of the deck, count that many cards into a face-down pile on the table.

5. Ask your dupe to add the two digits of his/her number and state the sum.