Cool Card Trick

When I went to Tech Trek I learned this cool card trick that works every time. I am still trying to understand the mathematics of it. All you need is a 52 card deck. The value of the cards goes A=1, 2, 3, 4, 5, 6, 7, 8, 9, 10, J=11, Q=12, K=13.

In the end, there will be three piles in front of you, two with their top cards face up and one with its top card face down. You will count the number of cards in your hand and know the value of the remaining face-down-top-card.

Setting up the piles:

1. To start a pile you put the top card of your shuffled, 52 card deck down on the table, face up. You count the value of this card, then place down cards until you get to 13. 
1. For example, if you pull an 8 of Spades, then you count that as 8. Then you would place 5 more cards down face up, regardless of their value. Then you flip the pile over so you can no longer see any value or suit. 
2. Here's another pile: Say you start with the 4 of Hearts. You count that as 4, then place down 9 more cards face up, regardless of value. 
2.  You continue creating piles until you can't. For example, say you have one card left in your hand. If it's a King, you count it as 13, and make a one card pile. If it's not a King, you keep it in your hand. Or say you have 3 cards remaining in your hand. You pull the top and it's a 5. You don't have enough cards to complete the pile, so you hold the 3 cards.

The Beauty of It:

1. Now that you have your 4+ piles, you select three. 
2. Then you pull away the rest and reincorporate them into the deck you hold in your hand of the remaining cards. 
3. You count out 10 cards and put them into a discard pile. 
4. Then you flip over the top card of one of the piles. You discard the amount of cards of the value of the top card you just revealed. 
5. You do the same with another pile; Flip over the top card and discard the corresponding number of cards.
6. Now, if you count the number of cards in your hand, that will be the value of your remaining face down top card!