Why Does This Card Trick Work?

[anaxcrosswords]

There's an arithmetical reason but it's beyond me! Here's how it works:

Randomly select 9 cards from the deck, face down. Turn them over and ask your guest to select one - you also see this card.
Put the other 8 cards face down, and their selection on top. Add the rest of the deck.
From the top, you create the first of four piles of cards, counting down from 10 to 1 as you do so. If the pip value of a card matches the number you call, you stop (court cards = 10, Ace = 1). If there are no matches, you deal an 11th card face down so the pile doesn't 'count' (I'll explain in a moment).
When you have created four piles, you add up the visible pip values. Let's imagine the total is 16.
Pick up the rest of the deck and count out 16 cards. The last one will be the player's selected card.
If there were no matches, i.e. each pile is topped with a face-down card, the first card of the remaining deck will be their selection.
This last bit is numerically inevitable, but I can't work out the significance of the cards which match the called numbers and are added up, because it seems to be random. Any ideas?

[anaxcrosswords]

Ignore the above - it just clicked!

[Gfrog]

Please explain then because you've baffled me :)

[cupid04]

I can't explain. I've sworn allegiance to the magic circle.....

[tandh]

lol this is one random post, i'm with g frog

[anaxcrosswords]

Before you start dealing the four piles of cards, the chosen card is the 44th (I think) one in the stack. What matters is it's always in that position.
When you start dealing the 4 separate stacks, if you don't get any matches you will have 11 cards in each pile, so the final one will be the chosen card.
All that happens when you DO get a match is that you add the number of cards you don't have to deal to the number you count at the end. Because, eg, if you start counting the cards 10, 9, 8, and the next card is a 7, you don't have to deal the next six cards plus the face-down 'stopper', ie 7 in total.
It's just a case of reaching the same number (44) via addition or subtraction.
Took me a long time to realise, so it's a very good trick.

[Lunol]

Is this a trick or is this known in gambling as "Card counting" which is banned and I think illegal in many gambling establisment across the globe immsmc.

[anaxcrosswords]

LOL - no, it's just a simple card trick, designed as something you could pull off among friends but not if you were a serious illusionist.

I've found another one, by the way, which still baffles me, but I'll try to work it out rather than embarrass myself with it here.