Name the two cards

Still quite a simple trick, which is able to puzzle many viewers. For his performance, you must have a small mathematical thinking. Take a deck of cards and ask the audience to hand over any 20 cards face down. Then ask another spectator, that he was of the 10 pairs of cards, that is, laid out 10 stacks of cards on the two cards in each pile face down. Then ask another spectator, that he looked map and memorized a couple of cards. Then collect all 20 cards: collect them in no particular order, but without separating pairs of cards and place them in the clear as follows.

The same figures are a couple of cards. For example, the numbers 1-1 is the first pair of cards, numbers 2-2 is the second card pair. All you have to do is to know in which row or rows are spectator card, which they remembered. Now you can get these cards. Looking at the chart, you will see that each of the ten pairs is different. Two cards of the first pair are in the front row, and if the viewer would say that both of his cards are in the first row, then you take a 1-1 card, if he says that the cards are in the third and fourth row, then you take a card 9-9 etc. If you are asked to perform the trick again, you need to change the scheme of disposition of twenty cards, but in a similar way. This trick may be performed with any number of cards. For example, a pair of twenty-one cards alignment of the scheme will be as follows.