A blind man is given a deck of 52 playing cards. All of the cards are face down and the man is told that this is the case. Ten of the cards are then randomly chosen and turned face up. How can the man divide the cards into two piles and ensure that that each pile has the same number of cards facing up?
If you have not tried to solve it, have a go now. For everyone else the answer is after the break.
The man divides the cards into piles containing 42 cards and 10 cards, and then turns the whole pile of 10 cards over. Did you solve it? Any other solutions?
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