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Think of a Number

No setupFull 52 Some counting10 min to learn

Somebody thinks of a number, takes that many cards off the top, and keeps them. You show them eighteen cards and ask them to remember the one that lands on their number. You never learn the number, you never see their card, and you never touch the deck again in any way that matters. Three piles dealt from ten down to one find it.

The number they choose is a real choice and it cancels out. That is the part worth understanding, and the reason this trick survives a spectator who is actively trying to catch you.

Play it through

Be the spectator and you think of the number, and it finds your card without ever asking what you chose. Be the magician and it thinks of one: you show the cards, you place them, you deal every pile and call every match yourself. Nothing stops you getting one wrong.

How to perform it

  1. Have the deck shuffled, and take it back. Nothing is set. Nothing needs to be.
  2. Ask them to think of a number from 5 to 18, and to take that many cards quietly off the top and hold them. Do not watch, and do not count.
  3. Show eighteen cards, one at a time, without reversing them. Take the top card, turn it towards them, and take the next one underneath it, and the next under that. Say the count out loud. Ask them to remember the card that falls on their number, and to give nothing away when it does.
  4. Put the eighteen underneath the rest of the deck. This is the move, and it looks like tidying up. Then take their packet back and put that underneath as well. Their card is now thirty-fourth from the top.
  5. Deal a pile, counting down from ten. Turn cards face up onto the table saying "ten, nine, eight" and so on. If a card matches the number you say — a six as you say six — stop that pile. Aces are one and court cards are ten.
  6. Do that three times. If a pile reaches "one" with no match, put a single card face down on it to kill it.
  7. Add up the face-up cards that matched. Count that many cards off the deck, and turn over the next one. That is their card. If no pile matched at all, it is the card on top.

Why the number they choose does not matter

This is the part worth knowing, and it is two facts that were built to meet.

The setup always leaves their card in the same place. Say they take n cards and you show eighteen. Their card is the nth of those eighteen. When the eighteen go underneath, the cards still in your hand — thirty-four minus n of them — sit above, and their card sits n minus one further down. Add those together and the n cancels: thirty-three, so their card is thirty-fourth. Their packet then goes underneath everything and changes nothing above it.

They think ofCards above theirs after the setupTheir card is
529 left in hand, then 4 more34th
1123 left in hand, then 10 more34th
1816 left in hand, then 17 more34th
Checked against every number from 1 to 18, on thousands of shuffles. The landing position never moves.

The ending always finishes in the same place too. A pile that matches on a six has eaten five cards; on a two, nine cards. In general a pile that matches on v eats eleven minus v. A pile that misses eats ten, plus the one you kill it with — eleven. So three piles eat thirty-three minus the total of the matches.

Then you count that total back. Thirty-three minus the total, plus the total, plus one for the next card, is thirty-four. Whatever the piles do, they hand back exactly what they took.

The limits, and why they are where they are

Both halves of this trick are fixed by the number of piles you deal, so it is worth knowing what you can and cannot change.

Piles you dealThe count finishes onSo you must showHighest number they can pick
One12th40 cards12
Two23rd29 cards23
Three34th18 cards18
Four45th7 cards7
Three piles is the version worth performing. Two piles buys five more on the number, 23 instead of 18, and costs you showing 29 cards one at a time — a long while to hold a table. Four piles is quick and the number is too small to impress anybody. One pile is worse than it looks: you show forty cards and they still cannot pick higher than twelve.

Two things set the ceiling, and the smaller one wins. They have to see their card, so their number cannot be higher than the number of cards you show. And the deck has to still hold that many cards after they have taken theirs, so their number cannot be higher than fifty-two minus the number you show.

For eighteen shown that is the smaller of eighteen and thirty-four, so eighteen. Nineteen puts their card somewhere you never turn over. For twenty-nine shown it is the smaller of twenty-nine and twenty-three, and there the second limit bites first.

The floor is not arithmetic. One works perfectly well. But a card shown fourth arrives before somebody has settled into not reacting, and a person who has taken two cards off the deck feels like they have done nothing. Five is where the choice starts to feel like a choice.

The one thing that goes wrong

They miscount. If they take twelve cards and remember the eleventh card shown, you will name the card next to theirs, and there is nothing you can do about it in the moment.

So make the count easy: say the numbers out loud as you show the cards, slowly and clearly, and let them take their packet without hurrying.

Jokers raise the ceiling, one each

Every extra card moves the setup on by one. Fifty-three cards means showing nineteen, their card still finishes thirty-fourth, and they can think of any number up to nineteen. Two jokers takes it to twenty.

A joker in the counting piles matches nothing, and that changes nothing: a pile that misses is already paid for by the card you kill it with.

Where this comes from

This is Easy Location by Aldo Colombini, published in his book Impromptu Card Magic. Colombini credits it as an adaptation of a routine by Richard Vollmer, which was itself based on a trick published in John Scarne's Scarne on Cards in 1949. The ten-to-one count underneath all of them is older still and has been in print for decades.

Two things here are not theirs. The spectator thinks of a number and removes that many cards, where the published handling has them cut a packet and count it privately — the same arithmetic, a cleaner premise. And the limits set out above were worked out from the mechanism rather than taken from anybody: the ceiling of eighteen, the floor of five, and the fact that two piles would let somebody pick a number as high as twenty-nine.

The explanation and the demonstration on this page were written from the method, not from Colombini's text. If you want his handling in his words, his books are still sold and worth buying.

Questions people ask

What is the think of a number card trick?

Somebody thinks of a number, takes that many cards off the deck, and remembers the card at their number while you show a run of cards past them.

You never learn the number and never see the card. Three piles, counted down from ten, find it.

How does the think of a number card trick work?

Showing eighteen cards puts their card thirty-fourth from the top, and the number they chose cancels out of the arithmetic completely — that is the whole idea.

Then three piles counted down from ten eat thirty-three cards between them, minus whatever the matches came to. Count the matches back and you finish on the thirty-fourth card, every time.

What numbers can they choose?

Any number from 5 to 18. The upper limit is arithmetic: you show eighteen cards, so eighteen is the highest number that can still be inside them.

The lower limit is a performance choice. One or two works perfectly well and looks like nothing, because they have barely taken any cards.

Which mistakes actually break it?

Only one: showing the wrong number of cards. Eighteen is not a choice, it is 52 minus 34.

Missing a match, or stopping a pile on a card that is not a match, both survive — each pile accounts for exactly eleven cards whatever it does. Those are mistakes the spectator sees, not mistakes that lose the card.

More

The 21 card trick also finds a card without being told anything — but it narrows down to one, where this one puts a card in a fixed place and then walks to it.