📝 The Answer in Advance

The Answer in Advance for kids: the whole trick

A friend writes any four-digit number to start a sum, and you write something on a paper and fold it up. Two more friends add a line each, and you add a line after each of theirs. Somebody adds it all up, and the answer matches the paper that was folded before the sum was finished. It's a level 2 conjurer trick for ages 8 to 13 (grades 3rd–7th), takes 15 minutes to learn, and needs 2 things you already have. Flick, the shop's rabbit, reads every step aloud with a picture, so a child can follow it alone.

The secret

Each line you add makes 9 with the line above it, digit by digit, so each pair of lines adds up to 9999, which is 10000 take away 1. Two pairs add 20000 and take away 2, so you can write the answer as soon as you see the first number.

What you need

• A sheet of paper
• A wooden pencil

How to do it

1. Ask a friend to write any four-digit number at the top of a sheet of paper.
2. On the other sheet write your answer: their number take away 2, with a 2 in front.
3. Fold it up and give it to somebody to hold. Nobody looks inside.
4. A second friend writes another four-digit number under the first.
5. You write a line under it, choosing each digit to make 9 with the digit above it.
6. A third friend adds a four-digit line, and you add a make-9 line under theirs too.
7. Ask someone to add up all five lines carefully, or on a calculator.
8. Open the folded paper. It already says the answer.

Magic words to say

“I'm going to write down the answer to a sum that nobody has written yet. Then you three can write it. Let's see if the future gets it right.”

Pro tips

• Write your lines at the same speed your friends write theirs, so they look like any other number.
• If the first number ends in 0 or 1, taking 2 away needs a borrow: 4270 take away 2 is 4268. Keep four digits, so 1000 becomes 0998 and you write 20998.
• Give the folded paper to the person who will add it up, so they hold the answer the whole time.

If something goes wrong

If the total doesn't match, check each make-9 line first: every digit with the one above it must make 9. The slip is nearly always there, and it still feels like a mystery when it comes out right.

Safety notes

• Needs a helper.
• Sit at a table.
• No fire, no flames and nothing sharp in a child's hand anywhere in the Magic Shop. Nothing ever goes in a mouth, a nose or an ear.

Why it works

Each make-9 line turns the line above it into 9999. Adding 9999 is the same as adding 10000 and taking away 1, so two of them add 20000 and take away 2. That is why the answer is the first number with 2 taken off and a 2 in front.

What kind of trick is this?

🔮 Prediction. You knew all along, or you read their mind. Almost every trick ever invented is one of eight kinds, and knowing which one you're watching is how magicians work out how a new trick is done.

The skill it teaches: Working with helpers. A helper should walk away feeling brilliant. Perform it and it counts towards the Mind Reader badge.

Questions about the answer in advance

How do magicians read minds?

They don't hear your thoughts. Mind-reading tricks use maths that always lands on the same answer, a secret peek, or a code agreed with a partner beforehand. Magicians who do mind tricks are called mentalists.

How do magicians do their tricks?

Magicians use secrets. Some secrets are hidden objects, some are special ways of holding things, and some are clever maths. The biggest secret of all is attention: a magician gets you to look at one thing while the secret happens somewhere else. Then they practise until it looks like nothing at all.

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