I've always wanted to learn a magic trick to use on my inebriated friends...and now I've got one. In this Brain Games “DIY” segment, illusionist Max Darwin uses simple math to predict the location of a $100 bill on a table, as a person moves it around. He then proceeds to walk you through how to do it yourself! Have a look:

Note: I'm pretty sure the move at the 1:50 mark is technically illegal, though it worked out all right in the end due to pure luck. You might want to make sure your "mark" fully understands the rules before starting. I'd also recommend starting with something much smaller than $100 on the table!