How to Read Someone's Mind With Math (Math Trick)

Last Updated: April 4, 2022

Mathematics is governed by a fixed set of principles. If you follow the same process, you'll get the same answer every time. Using math in magic tricks, however, is just as much an art as it is science. Of course you won't be able to read someone's mind literally with these tricks, but if done correctly, you'll be able to wow your friends by guessing their answer without them telling you!

Part 1

Part 1 of 2:

Performing Mind-Reading Tricks

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1
Find a kind willing partner. Find someone you're looking to impress, who has a few minutes to spare for your trick. It's best to find somewhere quiet to do this, as an interruption risks messing it up.
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2
Ask him to pick a whole number between one and ten. In theory, they could choose any real number. However, it's best to stick between one and ten for the sake of simplicity. Larger numbers will complicate the math; so will choosing numbers with decimal points or fractions. ^{[1]
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3
Impress him with the "End With 3" trick. This trick is a good one to start with, as its one of the simplest. There's just enough substance to make it impressive however, so take the following steps and get them wondering how you knew it:
1. Tell him to multiply their number by 2.
2. Ask him to multiply the new number by 5.
3. Have him divide their current number by their original number.
4. Instruct him to subtract 7 from their current number.
5. "Guess" the answer! If the prior steps were done correctly, the right answer will always be 3.
6. Witness as the fabric of their reality crashes down around them.
- For example, if your friend chooses 3: 3x2=6. 6x5=30. 30/3=10. 10-7=3.
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4
Perform the "Divide by Half" trick. This one's a little more complicated, but it's a perfect way to keep impressing your friend. This time, you'll have to choose a number too, so have an even number in mind before you begin. Once your friend has chosen a number, follow these steps:
1. Tell him to multiply the chosen number by 2.
2. Choose an even number to use yourself. Ask your friend to add this number to the one in their head.
3. Tell them to divide the new number by 2.
4. Tell them to subtract their original number from the equation.
5. "Guess" the number. This time around, the right answer will be half the even number you chose.
- For example, if you choose 10, and your friend chooses 3, here's how the equation will go down: 3x2=6. 6+10=16. 16/2=8. 8-3=5. 5 is half of 10!
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5
Wow your friend with the "Lucky Number 13" trick. This is a great trick that operates on the unique property of multiples of 9. It's very important the number your friend chooses is between 1-10. Once your friend has picked a number, here's how to do it:
1. Tell your friend to multiply their number by 9.
2. Tell them to add the first and second digit of their number together. If it's a single digit number (i.e. 9), add 0.
3. Get your friend to add 4 to their new number.
4. "Guess" the answer. Each and every time, the answer will be 13.
5. Watch as they begin to question everything they once held close and dear.
- If your friend chooses 3, here's how the equation will unfold: 3x9=27. 2+7=9. 9+4=13.
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6
Add some panache to your performance. While the most important thing is that you get the steps down right, you're ultimately performing a magic trick for them, and magic requires a certain level of style. Giving your tricks a confident, theatrical presentation will make it more enjoyable for everyone.
- A magician's costume isn't necessary, but it might be handy in giving the impression you're imbued with magical powers.

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Part 2

Part 2 of 2:

Understanding the Math

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Understand that certain parts of each trick are smoke and mirrors. A large part of performance magic is in distracting your audience with otherwise useless steps and information. The core mechanic in a lot of these tricks is getting your friend to eventually subtract their given number from the equation. Once the variable is out of the way, you have full control over where the equation goes. ^{[2]
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2
Identify unique patterns and occurrences in mathematics. The reason why the "Lucky Number 13" trick works so well is because multiples of 9 between 1-10 operate under in a uniquely identifiable way. In the case, each answer (e.g. 9, 18, 27 etc.) will equal to 9 if you add each digit together. Although this property is unique to multiples of 9, it makes a great trick, especially if your friend was quick to catch onto the fact that other tricks are quick to discard the original number.
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3
Acknowledge that every answer hinges upon the constant information in the equation. Adding superfluous additions and subtractions can be done as many times as you want, so long as you're ultimately able to nullify your friend's chosen variable. For instance the "End With 3" trick can be rearranged to end with any number.
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4
Try inventing a trick of your own. Once you've had some time getting used to mathematical mind tricks, you might be ready to try crafting your own. While they can become as infinitely complex as you want, it's a good thing to start out small, and slowly work your way up. For starters, use the "End With 3" as a template, and change the values of the constants to make a new equation. From there on, you'll be able to create new and inventive ways of ultimately removing the variable. ^{[3]
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- Don't forget to consistently develop your presentation as well. People want to be entertained, and the way you baffle them with your trick is going to be just as important as the trick itself!

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Community Q&A

Question

Will this work if I use big numbers (like 50 or 100)?

Community Answer

Yes, but it will make the math more complex. Using 1 through 10 is a lot easier.
Question

Will this work with any number?

Phoenix XinX

Community Answer

Yes, but it gets more complicated as the number gets higher.
Question

How am I supposed to know the number he chose?

Donagan

Top Answerer

You're not. It doesn't matter which number is chosen. The "trick" is that -- done right -- the math allows you to find the number, whatever it is.

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Warnings

It's not a good idea to be doing mind-reading tricks with more than one person at a time. Not only does it get confusing; it also ruins the mind-reading fantasy.

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References

About This Article

wikiHow is a “wiki,” similar to Wikipedia, which means that many of our articles are co-written by multiple authors. To create this article, 61 people, some anonymous, worked to edit and improve it over time. This article has been viewed 1,281,816 times.

181 votes - 69%

Co-authors: 61

Updated: April 4, 2022

Views: 1,281,816

Categories: Magic Tricks | Mathematics

Article SummaryX

To read someone's mind with math, ask your partner to pick a number between 1 and 10. Tell your partner to multiply their number by 2, then multiply the new number by 5. Divide their current number by the original number, then subtract 7 from the answer. Finish by guessing the answer, which should always be 3. If you want to give your trick the appearance of being magical, wear a magician's costume and perform each step with a touch of theatrical flair. For tips on how to do the Divide by Half or Lucky Number 13 tricks, read on!

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