Why do I keep coming back to Scam School videos? Because they're so often an entertaining and effective way of learning mathematical concepts.

This week, Scam School teaches Bob Hummer's 3-Object Divination. This is strangely reminiscent of 3-card monte, but with a mind-reading twist.

Watch the video below, and see if you can work out the method before watching the explanation (Stop on or before the 5:27 mark):



Were you able to work out the method? Whether or not you were, finish watching the video, and make sure you understand the method.

There are several great things about the routine. First, it's a great example of how even simple logic can be made to appear as a near-impossible feat. Second, because the logic is the method, you can (as noted in the video), apply this principle to any three objects. You could play this big and use large objects on a stage, if you so desired.

This trick was originally marketed by Bob Hummer in 1951 as "Mathematical Three-Card Monte". You can read more about the original version in Martin Gardner's book, Mathematics, Magic and Mystery. Thanks to Google Books, you can read about it online for free: Part 1, Part 2, Part 3.

Notice in Bob Hummer's original version, you don't turn around. Instead, you have them call out the objects as they're switched, then turn around. Depending on how you're presenting this feat, this touch may make it more or less impressive. Having the moves called out can make it seem more technical, while watching the moves has a more casual appearance.

Since Bob Hummer's original version of this routine, there have been some great thinkers turning their minds to this very routine. Harry Lorayne has developed a nice addition to this routine where you never turn around to examine the objects (this version can even be done over the phone!). This was originally published in Martin Gardner's Sixth Book of Mathematical Diversions from Scientific American, and is now also available in Harry Lorayne's own book, Mathematical Wizardry.

Magician Max Abrams developed a great version of this classic, but routined it as a test of the spectator's ESP. It features the interesting twist that the performer mixes the cards, yet is still engaging. It also comes across less as a puzzle, and more as a shared experience. It's called Hummeracle!, and can be found in the March 1990 issue of Genii magazine.

Take a deeper look at this great routine. It's well worth your time.