There's a long lost PBS show called "Square One TV" (I understand it resurfaces on Noggin every so often) that occasionally featured a segment called "Backstage With Blackstone".

Since "Square One TV" was all about math, each of these segments featured Harry Blackstone, Jr. performing a trick with a mathematical basis, and then explaining it. Until today, I hadn't been able to find a single video online of any of these segments. You've probably all done a similar effect at some point, but it's fun to watch anyway.

Here it is: Backstage With Blackstone - Five-Envelope Elimination

Yeah , its similar to Copperfields pick an object !