# Mind reading number trick: How to guess a spectator’s number

This trick allows you to read the mind of a spectator by guessing his selected number. The great thing about this method: the other person can choose literally any number between 1 – 10.000 (but keep in mind that you might need a calculator if the number is too high). How does this mind-reading number trick work?

A spectator may choose any number and multiplies it by “9”. From this result, he crosses out a digit of his choice and reads all the other digits to you – and you can immediately name the crossed-out digit.

## How this mind reading trick works: an example with a random number

To help you understand this magic trick, I’ll first show you an example with a number from the viewpoint of the audience. You’ll find the explanation right after that and you can do the trick right away.

• Let’s assume that the spectator chooses the number 2,178 (it can be any number, more about that later).
• Now he multiplies this number by 9, so: 2.178 x 9 = 19.602. From this number, he may choose any digit (it doesn’t really matter which one he chooses).
• The spectator chooses any digit, in this example, I choose the digit 2 of the spectator number 19,602.
• Then the spectator names all the other digits in any order (except for his chosen digit), so in this case he says for example: “0 6 1 9”, but he could also say “1 9 0 6” or “9 6 1 0” – it doesn’t matter.
• Only with this information, you can immediately say that the chosen number of the spectator must be the digit 2.
`Quick tipThe procedure looks more complicated at first sight than it actually is. The spectator is already finished after only one calculation - this way, the magic trick stays nice and short.`

How this works and how you can perform this mathematical magic trick, you will learn right here. The spectator can actually choose any number, no matter how big it is.

## Guessing the spectator’s number: how it works

This trick is quite simple in itself, but there are a few details you should pay attention to. First, the explanation (I’m again using the number 2,178 from the example above).

Here’s an image of the entire process:

### Guess the number of the spectator – explained step by step

• You form the checksum from the digits that the spectator tells you. In our example, these are 0, 6, 1 and 9, so the checksum is 0 + 1 + 6 + 9 = 16.
• Then you find the next multiplier of 9 (i.e. 9, 18, 27, 36, 45, 54, …). In this case it is 18.
• To find the number of the spectator, you just have to subtract the cross sum from this multiplier. In our example: 18 – 16 = 2, the chosen number of the spectator!

Please read: For this magic trick to work, the spectator must not choose zero as “his” digit, but a number between 1 – 9.

### Special case (in case the cross sum is 9)

The sum of the spectator’s digits maybe 9. If this happens, the chosen digit is always 9.

An example: The volunteer chooses the number 133 and multiplies it by 9, so 133 x 9 = 1.197. If he then chooses 9 as “his” number, the cross sum is 1 + 1 + 7 = 9.

So remember: If the checksum is 9, the spectator has also selected the number 9!

## A few tips for performing this number trick

You must get the effect of this trick right. You don’t have to see the spectator’s number at any time, which means you can even blindfold or turn around.

Keep in mind: The spectator must never select the number 0 because then the trick won’t work.

So, say something like this:
“Pick a digit between 1 – 9 and mark it without saying anything. Just don’t pick a zero if there is one in your number – that would be too easy.”

Also, you only need the spectator’s digits for checksum, which means he can tell you them in any order. Emphasize that properly and put the focus on it! Example:

“I can’t possibly know your chosen number, you may even read out the individual digits in a jumble. So there’s no way I can know what number you chose.”

Your audience doesn’t know that you’re simply forming the sum of the digits – so in their eyes, you can’t figure out the digit you chose.

By the way, if you are looking for more number tricks, you can check these tricks:

## In short: The most important things to keep in mind

• This magic trick really works with all numbers, no matter how big they are.
• The spectator can name the numbers in any order (you only need the sum of the digits). Sell this cleverly to the audience (example: “I can’t possibly know the number, you may even read out the individual digits in jumble”).
• Remember that the audience must not choose the number 0, then the trick won’t work!
• If the cross sum is 9, the number chosen by the spectator is also 9.
• The bigger the number of the spectator, the more numbers you have to add for the cross sum. You can tell the volunteer before the trick that the number should not have more than four digits (i.e. stay below 10,000).

Have fun performing this little math trick!

Looking for another mind-reading trick? With this illusion, you can predict the words chosen by someone from the audience!