Postby Guest » September 8th, 2006, 6:57 pm
The odds of any card being at any number appear at first to be far smaller than they really are. That's exactly what we want the spectators to think, of course!
It's very simple: Think of any card. Now - how many possible positions are there for that card within a shuffled deck (from the top)? Only 52. No more and no less. So when you then name a number, the chances that your card occupies that position are 1 in 52. This applies no matter which card you originally think of.
Because each card actually occupies TWO positions - one from the top and one from the face - (e.g. 8 and 45), then if you do the trick by counting from either the top or the face, the odds of your card being at your number are 1 in 26.
If you do the trick, as Dave Le Fevre suggests, by counting from the top or the face, and taking either the card AT the named number or the one immediately AFTER it (all of which options can be presented in an entirely logical way) then the odds get even better. However, the odds in this case are, strictly speaking, slightly less than 1 in 13 because for positions 1 and 52, there is no option to count to the card AFTER the number. (i.e. if the spec names "1", you can't say, "ok - count off zero cards and look at the next one". Similarly, if he says "52" you can't say "ok - count off 52 cards and look at the next one").
Making use of these odds (and to avoid much/any manipulation of the deck with sleights) would require stacked decks that cater for each possible card-number combination using these different counting methods. The various approaches to devising and handling such stacks is an area where, no doubt, David Berglas's thinking and experience applies. The stacked decks would enable the effect to be done by selecting the deck to be used after the card and number are named (as Paul Gordon describes David Berglas doing for him).
In cases where the cards are "out at the top" (with no room for manipulation of the deck before the spectator himself counts down to the card)... I repeat what I said earlier about luck, and the option to take the routine in a different direction entirely if luck does not go your way.
Richard, in your description of the effect...
"When Berglas did the effect for me, he never touched the deck.I named a card, I named a number, he pointed to the deck. I took the deck out of the case and put it face up on the table (at his instruction). I counted down to the number I named and my thought-of card was there. BAM."
...you happened to name a card that lay at the number you chose (from the face).
If someone does the effect for me (in this "cold" scenario where it's just me and him and a single deck) and needs to do a casual cut (or some other kind of handling of the cards) before or during the count, the effect is not going to be too impressive. However, in a group setting, in the context of other magical effects that are ocurring, and with the right sense of showmanship, direction and timing, such a method (as is discussed in TMAMODB) could of course be used.