Magic Tricks

I got this trick from William Simon's book "Mathematical Magic" and have used it whenever I do math-magic at STEM events and science fairs, including the National Math Festival in DC last April. I bought the trick because I thought that it might have been a little different, but it wasn't. However, the presentation is different than what I use, so it is good to have some variety when doing a particular trick. Only the best math students and adults can figure out the trick while standing before me, and the rest are pleasantly puzzled. Works for kids who can do arithmetic in their heads. Generally, 11 or 12 is a good age.