card trick (thing)

First, you need some supplies. Namely, a deck of cards. If you'd like to play along at home, go get one now. I can wait.

*taps foot whilst various Everythingians scramble to get some cards*

Okay, dandy. Let's begin.

This is a cool 'find that card!' card trick, where you'll be able to tell someone what value the top card of a pile (you get to make piles, too! Funfun!) is. There's most likely something mathematical involved, (and, from looking at the other card tricks here on E2, it probably involves modulus stuff), but I'm not sure what it is. If anyone knows, I'd be much obliged if they'd node it here as well.

So anyway, on to the trick!

Flip the top card of the deck over, so it's face-up on the table/desk/floor/ceiling/whatever available, reasonably flat surface you happen to be by right now. I'll do it too, to demonstrate:

 _________
|7        |
|♥        |      
|         |     Well, lookee here, I got a 7.
|         |
|        ♥|
|        7| 

A quick refresher for those that don't play with cards much (like me - I had to count the silly things out myself before noding this): there are 4 suits of 13 cards each in a standard 52-card deck. The cards are valued (at least in this trick - sometimes the Ace is the highest) Ace (1) through King (13). Remembering this is of utmost importance.

Since I got a 7, I'm going to add 6 more cards to the pile.

A somewhat understandable equation for this:

13 - (Card Value) = # of new cards to be added to the pile
(again, note that Jacks have a value of 11, Queens are 12, and Kings are 13. Aces are 1s)

Okay, so, 6 more cards it is:

 ___________________________
|7 |6 |K |8 |7 |4 |J        |    
|♥ |♥ |♠ |♣ |♦ |♣ |♦        |
|  |  |  |  |  |  |         |
|  |  |  |  |  |  |         |
|  |  |  |  |  |  |        ♦|
|  |  |  |  |  |  |        J|

 _________
|         |
|  Back   |      
|   of    |   Now doesn't that look pretty?
|  Pile   |
|         |
|         |

If you have leftover cards, simply set them aside or hold them or something. They aren't a pile. They didn't make the cut. They are rejects and losers, and you don't want anything to do with them. For now. You will later, so don't ostracize and taunt them too much or they'll figure out some way to screw you over at the end of the trick.

Here's the fun part: pick up all the piles except for 3. Put all the picked up piles in a stack with the leftover cards from before, and turn up the top cards on two of the remaining piles.

Here's another one of those nifty ASCII visuals of this:

 _________       _________       _________
|         |     |10       |     |8        |
|  Back   |     |♠        |     |♦        |
|   of    |     |         |     |         |
|  Pile   |     |         |     |         |
|         |     |        ♠|     |        ♦|
|         |     |       10|     |        8|

Here's how you do it. With your uber-pile made from all the other piles, start counting out cards. In the example above, you'd count out ten cards, then eight cards, and finally ten more cards. This is because of the top cards on the other two piles are a 10 and an 8, respectively. Then, no matter what the top cards are, you always count out another ten afterwards. This probably has to do with math of some sort.

You should be holding the rest of the uber-pile now. Count the number of cards remaining and you've got it. That's the number of the card on top of the last pile.

Pretty neat, huh?

Some tips for preforming this trick for others:

• Let the victim/audience member/whatever you want to call 'em do things like shuffle your deck before the trick and the uber-pile, choose the piles to get rid of, et cetera. This lets them think you care about them and their meaningless decisions. Shuffling the deck and letting them pick the piles doesn't change anything. It's all good - you can still dazzle them with your mad magic skillz despite their best efforts to screw you up.
• Make sure your card counting is silent and fluid, so it doesn't look like you're making uneven piles on purpose. It should, when you have it down to a science, look like you're just randomly scattering cards into piles across the table. This makes it all the more impressive when you can figure out what their card is because no one's sure you have any idea what the hell you're doing.
• And finally, as with all "magic," practice, practice, practice!

Oh yeah, and have fun. :)