Read this tip to make your life smarter, better, faster and wiser. LifeTips is the place to go when you need to know about Performance and other Magic topics.
Here is a surefire force that takes place in the spectators hand. Beforehand, select the card you want to force and place it as the ninth card from the top in the deck. You're now set to begin.
Casually shuffle the deck, being sure not to disturb the order of the top nine cards. Give the deck to the spectator and ask them to deal off, face down, any number of cards between ten and twenty. If they choose twenty, remind them that the instructions were any card BETWEEN ten and twenty.
Once the cards are dealt face down, ask the spectator to add the two digits of their chosen number together to arrive at a single digit. (If they chose 15, for example, then 1 and 5 is 6) Now, ask them to pick up that many cards off their dealt stack and place them back on top of the deck. The next card on top of their dealt stack is to be their selected card. Your force is complete as this is also the card you placed in the ninth position before the force began.