Twenty Card Magic Trick

The Effect: The magician sets twenty randomly selected cards
on the table, face up. While the magician is out of the
room, each of the spectators mentally select a different pair
of cards. The performer randomly places the cards in rows
of five. Each of the spectators point to the two rows that
their cards are in, and the magician immediately picks up
their pair of cards.

Secret: The cards are not actually placed at random and
instead a formula is used to place them in a special self working
pattern. Imagine that you see these four rows of
words spelled with big letters across the table: start, bells,
brooz, and dazed. Start by placing the first pairs of cards
on each imaginary S, then on each T, and on each A and R.
Continue going down the rows, placing the each of the
pairs of cards on the next pair of letters in the formula.
Now as the spectators point to the rows their two cards are
in, you pick up the only pair of cards in these rows.

Method: Practice placing the cards in this formula, until
you can do it fast enough to look natural. Place the twenty
cards in pairs on the table first, leave the room, and ask the
spectators to select their pair of cards. Do not put them in
their special order until you have re-entered the room. This
will also give the spectators less time to over think the
entire process. When you enter the room, pick up the cards
and quickly lay them in the special order. Now if they say
their item is in the first and last row you know it is the
object in the place of the letter A. If their item is in the
second and third rows, then the letter B will be your key.
You will notice that you do not necessarily need to use the
letters to find the pairs, simply use the formula to place the
cards in their self-working location.