In last month’s puzzle (submitted by SQL Server MVP Steve Kass), you had a deck of 52 cards, faces down. You turned over 7 of the cards so that they were face up, then shuffled them into the rest of the deck. Your challenge—while blindfolded—was to separate the cards into two piles such that each pile contained the same number of cards facing up. The number of cards in each deck didn’t have to be the same, only the number of cards facing up.
This puzzle is mathematical in nature. Split the deck into two, such that the left pile contains 7 cards and the right pile has the remaining 45 cards. The left deck contains a certain number of cards facing up (call it n), and the right deck contains the rest of the face-up cards (7 - n). The solution is to turn over all the cards in the left deck. Because the left deck had 7 - n cards facing down, when you turn them all over, you're left with a deck containing 7 - n cards facing up. Now, both decks contain 7 - n cards facing up.
Check out the May issue for the next Logical Puzzle challenge, Basic Arithmetic