Cards - 1

A blind man is handed a deck of 52 cards and told that exactly 10 of these cards are facing up. How can he divide the cards into two piles, not necessarily of equal size, with each pile having the same number of cards facing up?

Solution:
Blindman makes 2 piles, P1 - 42 cards  and P2 -10, He then flips all the cards in P2.

Example : If there are 6 cards facing up in P1 and 4 in P2 after the split. When he flips all the cards in P2 he will have 6 cards facing up and 4 cards facing down - Hence both the piles have the same number of cards facing up.