Card Trick but its not a Trick


Silver Level Poster
I'm not sure how this works but if anyone can answer it then I would be interested to hear from them.
1. Start with a full pack of cards.
2. turn the top card over if it is say a 6 then count out 7 other cards to add up to 13.
If the card was a 2 then add another 11 cards again to make 13. A Queen or King count as add three cards to make 13.
3. Make 6 piles of these cards so each pile adds to 13.
4.After you have made 6 piles keep the remaining cards in your hand.
5. Ask someone to pick out the 3 biggest piles of cards for you and add these to the ones in your hand.....this will leave 3 piles of cards
6. Then ask them to turn over the top cards from 2 of the 3 piles remaining.
7. You will tell them what number the other top card is in the 3rd pile.
8. You do this by adding together the 2 cards they turned over, say they were a 6 and 9 = 15 then add 10 = 25. (you always add 10 to the number of cards at this stage)
9. Count out 25 cards from the pile in your hand and whatever number of cards are then left in your hand = the number of the 3rd card once it is turned over.

No trick but how does it work.