Magic Tricks

Someone above was dismissive of the maths involved in these tricks. I see it differently - the fact that the maths involved is actually not overly challenging makes the routines themselves really clever - developing these tricks required insight and ingenuity. I've yet to "perform" these tricks but I'm confident I will be able to do so.
Money well spent.

I'd really appreciate any more maths based tricks - as a teacher I like to liven up my classes / challenge the kids to work out how tricks work. I'm always on the hunt for more material.