image creditA magician takes a deck of cards, and gives it to you, and asks you to shuffle the cards as many times as you want, and asks you to give the cards back face down. The magician takes the cards and counts them out into two piles without looking at any of the cards. He now says 'I've made two piles so that the number of red cards in the first pile is the number of black cards in the second pile.' You turn the cards over, count the reds in pile one, the blacks in pile 2, and see that it’s true.
How did the magician do this trick? You can find the answer here.
