Card trick

Supplies:
21 cards, all different

Secret:
First lay out the cards, 3 across and 7 down.

Have someone think of a card and tell you what row its in.

Pick up all the rows, row by row, making sure to pick up the row that the card is in 2nd. do this three times. on the third time, pick up the the 4th one down in the row the person said the card was in