The Principle of Nine is probably as old as mathematics itself. Take any number, say, 127. Add the digits of the number together: 1 + 2 + 7 — 10. Finally subtract the result from the original number: 127 - 10 — 117. The final answer is always a multiple of nine. The name of the person who made the leap to playing cards appears to be lost, though Royal V. Heath has been mentioned. Certainly, Stewart James and Bob Hummer were pioneers in the field, both working along similar lines, often combining Estimation with the principle and producing ingenious results.
The basic estimation principle:
1. Place the deck on the table. A spectator cuts off any number of cards. You glance at the packet then turn away. Estimate the number of cards to within a ten card group: 10's, 20's, 30's or 40's. Let's say you guess the number is within the twenties range (20 - 29). The last multiple of nine prior to this range is 18. Remember that.
2. Have the spectator count the cards, then add together the two digits. Assuming he has 27 cards, his final answer will be 9. Ask to deal nine cards back onto the deck then look at the last card dealt.
3. Finally ask him to shuffle any cards remaining in his hand and drop them on top of his card. There are now 18 cards on top of his card and you can use this information in any way you like.
The Count-Back Force:
This is probably the most common use of the principle. In fact Al Koran won an originality competition with a trick using this very principle (reprinted as "Koran's Double Out Prediction," Sharpe's Expert Card Mysteries, 1975).
1. Place the card you want to Force at position ten from the top (one more than the multiple of nine).
2. Ask someone to think of any number between ten and twenty and to deal that number of cards into a pile on the table.
3. They now add together the two digits and count this number of cards from the tabled pile back onto the deck. They look at the card now on top of the deck—this is the force card.
The Less-counting Principle:
A twist on the principle that positions a card at the spectator's number while the spectator only uses the digits of his number. Here is an example without any presentational dressing:
1.Note the ninth card from the top of the deck and crimp the bottom card. Write the name of the ninth card as a prediction. Give the deck to a spectator.
2. Tell him to cut off about half the cards onto the table. Now ask him to think of any number between 10 and 20—this will be his "magic number." Tell him to add together the two digits and transfer that number of cards from the top of his packet to the bottom, then to drop his cards on top of the tabled half to complete the deck.
3. Pick up the deck and cut the crimp back to the bottom. Now ask him to count down to the card at his "magic number." This will be the card you predicted. (See "51 Faces North—The Peter Duffie Solution," The James File, 2000, for more on this version of the concept).
The three tricks that follow exploit the principle in different ways.
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