Fun Facts

How to accurately guess your friends age

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Throughout the ages men have been interested in mystery and in things that are strange, interesting and starling. As in the past, modern magic derives much of its charm from the phenomena which superficially are perplexing. With the maturity of mathematics, a term so called ‘Mathematical Magic‘ had come into its own in 20th century. There were mathematical geniuses behind this term who had those extraordinary qualities which were not possessed by others.

In these days of mind games and puzzles, mathematical logic should find an enthusiastic response. As the mathematical logic has some reasoning behind it. It is totally based on mathematical proofs. The logic which first seems to be unbelievable and interesting to people when proved through mathematical facts becomes believable to people. That’s why I decided to make a series on ‘mathematical tricks‘ or ‘mathemagic‘ based upon the power of ‘mathematical logic’.

In this post I want to share a simple math trick with you. By using this trick, one can easily guess the age of other person. You can use this trick in a way you like. You don’t need to follow my scenario rather you just need to follow the steps of this trick and then you can apply it to your preferred scenario which best suits you.

Let’s say I want to guess my friend’s age. This is my assumed scenario. I would request my friend to follow these steps sequentially.

Steps to follow

  1. Write down any 4 digit number of your choice on a paper.
  2. Transpose the digits of this number in any way you like.
  3. Now you have two numbers, one is original number and other one is the transposed version of that number. Subtract the smaller number from the larger. Then add up the digits in the resulting number.
  4. If you find this total to contain 2 or more digits, keep adding these digits together until you have only 1 digit as a final result.
  5. Add 7 to this resulting digit.
  6. Now request your friend to add the last two digits of his/her birth year in this total.
  7. Last step is to ask the final result from your friend, then subtract 16 from it. The resulting number will be the birth year of your friend. Knowing the birth year of your friend you can easily guess how old your friend is.

How it works

It just happens that when you take any number (regardless of the number of digits), transpose it and subtract the smaller from the larger, the sum of digits of the resulting number will always be equal to 9 or multiples of 9. It is obvious that if you keep adding them together they will eventually be reduced to one number, that number must be 9. If you add 7 to this 9 and subsequently remove 16 (which you just did) the result is obviously zero. This zero plus the last 2 digits of the year in which you friend was born gives away his/her birth year or his/her age on or before December 31st of the current year.


Let’s take an example here, if I reach out to my friend and ask him to follow my orders. Then at first he chooses a four digit number(he can even choose any n-digit number, not only 4-digit number) but let’s say he chooses 4210. then he transposes(reorders) this number in any way. Let’s say he reorders it as 1204. then after subtracting the smaller number (1204) from larger number (4210), he gets 6003. He adds all the digits of this number i.e. 6+0+0+3 and gets 9 as result (If the result happens to be a multiple digit number then again he has to add the digits until it gets a single digit result which would always be 9. But he would not know about this. Only you know that the result would always be 9). Then he adds 7 to it ( You can allow him to add any number of your choice but then you need to subtract the same from the result. This step is optional but can be followed to make him difficult to guess). He gets 16 as a result. Now you ask him to add last 2 digits of his birth year in it. Let’s say his birth year is 1995, he adds 95 to 16 and gets 111. Upto now he has not told you any result of any step. but now you will ask him about the result and he will tell you the result is 111 then you just need to subtract that 16 from it, you will get 95 then you can make a straight guess that his birth year is 1995 and you can find his age after subtracting 1995 from the current year.

Note: The age you compute will be based on or before 31st December of the current year. So depending upon his birth month, you can get 1 year more of his age. But in order to predict accurately, you can ask him whether his birthday in current year is passed or not. If not, then you can subtract 1 from the result. That would be his correct age upto now.


That’s how you can guess someone’s age using this trick. Feel free to test it on anyone. Have Fun!!

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