Have a friend think of any number under ten. Tell him, without revealing the number, to multiply it by three. Then tell him to add one. Next multiply it again by three. Finally add the number to the first number he secretly selected.

For the last step in the puzzle, ask the friend to tell you the final number he arrived at after the mathematical applications. Put both hands against your forehead as if you are in deep thought. Then tell him the number he first thought of. It will always be the left-hand digit in that final number. - Bits & Pieces, July 22, 1993 (Magazine: BITS & PIECES http://www.epinc.com/)