1. Before doing this magic trick you need to separate the cards into red and black. The black cards should all be together and the red cards should be together, making them like two small decks.
2. Separate the decks and lay them face down.
3. Ask a spectator to take one card randomly out of each "deck", making sure he/she doesn't look at the deck.
4. Ask the spectator the memorize the cards, then put each one back in the opposite deck from which they took it.
5. Have the spectator shuffle each deck separately.
6. Take the decks up and tell them you will now find their cards.
7. Simply look through the red deck up and find the only black card in it. Same for the black deck.