The Magic of Mathematics: Amaze Your Friends

     

Maths isn’t always deadly serious. To prove it, here’s a card trick to amaze your friends in the pub. It was invented by Arthur Benjamin, a mathematician and magician at Harvey Mudd College in California.

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Take a pack of cards and deals the top 16 face down in four rows of four. Turn four of these cards face up. Call for a volunteer from the audience, who will repeatedly ‘fold up’ the square of cards, like folding a sheet of stamps along the perforations, until it ends up as a single pile of 16 cards.

The audience will decide where the folds occur. For instance, the first fold can be along any of the three horizontal lines between the cards, or the three vertical lines.

When the cards have been folded into one pile, the volunteer spreads them out on the table. Either 12 cards are face down and 4 face up, or 4 cards are face down and 12 face up. In the first case, the face-up cards miraculously turn out to be the four aces. In the second case, the volunteer takes the four face-down cards, and turnsthem over to reveal… the four aces.

Magic!

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August 19, 2010