Mentalism Effect with Paper Magic

Guess a Letter - Magic Trick by sulap
EFFECT
This is a game called mentalism. The magician distributed 21 letters and only mentally able to guess which was chosen by the viewer.
SECRET
Distributed 21 cards in a deck, face up, in three rows of seven cards each, as shown in the drawing, and in that order.
The viewer, you should consider a letter and tell you which of the three rows is. When I tell you, you pick the one you mentioned, for example the third, and pick it up. Then pick the other two, and then placed one above and one below. The row that the viewer has told you, it must be made between the other two. Turn around the whole package, letting it back up, and come back to deal the cards as before giving them back, so they are face up. Again must tell you the column in which this letter.
Repeat the previous step and return to distribute twice as much.
The fourth time, leaving you deal the cards back to light up and you take your magic powers and pointed to the letter left in the middle of everything, ie the number 11, which will be chosen by the viewer.