I Love Weird Stuff Like This


Shuffle a deck of cards and start dealing them face up one at a time into a pile, counting down from 10 as you go — that is, say “10” as you deal the first card, “9” as you deal the second, and so on. As soon as you say a number that matches the value of the card you’re dealing, stop dealing and start a new pile. Face cards count as 10. If you count down to 1 without finding a match, “kill” the pile by putting a card face down on top of it.

Repeat this procedure until you’ve dealt four piles. (If all four piles are “killed,” which is very unlikely, shuffle the whole deck and start over.)

When the four piles are finished, add the values of the cards at the top of each “living” pile. Call that sum k. Now deal k cards from the remainder of the deck, and then count the cards that remain.

There will always be eight.

(Martin Gardner, “Curious Counts,” Math Horizons 10:3 [February 2003], 20-22.) via the good folks at Futility Closet.