How To Use Mathematics To “Guess” Someone’s Age

Have you ever felt the urge to “guess” someone’s age? This urge is especially strongest when the person is too shy to talk about it. That’s where mathematics comes in handy. In this article, I’ll be sharing a nice little mathematical trick that will help you guess anyone’s age.

I’ll give you two variations of the same trick first. Then, I’ll explain how the trick works so that you can come up with your own variations. Are you ready to come across as a wizard in front of your friends? Let’s get started.

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The Trick to “Guess” Someone’s Age

The first thing you’ll need to do is get the person to play a game with you. You may tell the person that you have the magical ability to guess their age and that you can only share more if they agree to play. If you wish to play dirty with someone being too shy, you may choose to skip the topic of age altogether and say that you have the ability to calculate the person’s lucky number if they agree to play a game of numbers with you. This way, you’ll catch them off guard.

In any case, once the person has agreed to play the game, you may choose to follow one of the two procedures that I have laid out below.

Math Procedure to Guess Someone’s Age — Variation 1

1. You first ask the person to double their age in their mind without revealing their age to you.

2. Then, you ask them to add 256 to the previous step’s result in their head.

3. You now ask them to subtract 30 from the previous result.

4. Then, you ask them to add 5.

5. We’re almost there! Next, ask them to subtract 20 from the previous result. Again, all of this is only done in their head. They share nothing with you until this point. You are the only person speaking.

6. Finally, ask them to subtract 11 from the previous result. This is the final number. Ask them to say this number out loud.

7. Now, take this number and subtract 200 from it in your head.

8. Then divide the result by 2. This reveals the person’s age! Now, act as if you are in deep thought, and “guess” their age proudly and confidently.

9. Enjoy their reaction and act smug for added enjoyment!

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Math Procedure to Guess Someone’s Age — Variation 2

1. Firstly, ask the person to multiply their age by 10 in their mind without revealing their age to you.

2. Then, ask them to add 80 to the previous result.

3. After that, ask them to add another 100 to the previous result.

4. Then, ask them to subtract 70 from the previous result.

5. Almost there! Ask them now to subtract another 20 from the previous result. Remember, steps 1 through 5 are done by the person in their head, and you do not hear anything from them.

6. Finally, ask them to add 10 to the result from the previous step and say the resulting number out loud.

7. Take this number, subtract 100 from it, and then divide the result by 10. This reveals their age! Now, as in the previous variation, act as if you are in deep thought, and “guess” their age proudly and confidently.

8. Enjoy their reaction and act smug for added enjoyment!

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How Does the Trick Work?

Both the variations I described use the same math trick. In fact, there are infinite variations possible if you understand how the trick works. All you will need is knowledge of linear equations and basic high school algebra.

In the first variation of the trick, I came up with the following equation:

2x + 256–30 + 5–20–11 = y

This is just a plain old linear equation that relates the variables ‘x’ and ‘y’. Here, ‘x’ is the age of the person. They perform the left-hand side of the equation in their head to get ‘y’. Then, they say the value of ‘y’ out loud. In the meantime, I had already solved the equation for ‘x’ to get the following result:

X = (y — 200)/2

Therefore, when the person reveals the value of ‘y’, I just need to subtract 200 from it and divide that value by 2 to get their age.

In the second variation of the trick, I came up with the following equation:

10x + 80 + 100–70–20 + 10 = y

Like before, ‘x’ is the person’s age and ‘y’ is the final number they say out loud. If I solve this equation for ‘x’, I get the following result:

X = (y — 100)/10

Now, I just need to take their ‘y’ value, subtract 100 from it and divide the result by 10. And I have their age!

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How to Make Your Own Variations?

The key point to takeaway here is that you are working with a linear equation relating ‘x’ to ‘y’ (and vice-versa). When playing the game, you let the person solve for ‘y’ without revealing ‘x’ to you. In the meantime, you solve the equation for ‘x’ and wait for the person to reveal ‘y’.

Imagine that the both of you are trying to reach each other’s starting point from the opposite ends of a twisted tunnel. You are guiding the person through this twisted tunnel towards you. As soon as they arrive, you gain the ability to teleport to their starting point through a secret math hyperspace. Only you have access to this hyperspace because you designed it!

Once you understand this, you can let your imagination run wild, and create your own variations of the game. If you or your game partner is feeling adventurous, you may choose to work with non-linear equations (squares and the like) and make it more challenging.

Now that you are armed with this knowledge, you have gained the right to transform into a wizard at parties. As for me, I just hope that you keep this a secret between the two of us. Enjoy!

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Further reading that might interest you: How To Solve The Doubling Puzzle? and Why Do You See Mirrors Flipping Words?