Impress your friends with this cool mathematics puzzle. (and know how maths is useful in real life)

This lets you give the age of a person and the number of siblings in their family.

Questions that you need to ask

  1. Think of your age in years 
  2. Multiply your age by 2
  3. Add 10
  4. Multiply by 5
  5. Add number of siblings that you have
  6. Subtract 50 from this number
  7. What’s the number?

How it Works

If you know an animal called Algebra, this would be a cakewalk for you. How it works is this. Follow the questions….

Question                     Answer Example       Algebraic Equivalent

1. Think of your age in years         15          [10x+y]

2. Multiply your age by 2               30          2[10x+y]

3. Add 10                                       40          2[10x+y] + 10

4. Multiply by 5                              200          5{2[10x+y]+10}=100x+10y+50

5. Add # of siblings you have        203          100x+10y+50+z

6. Subtract 50                               153          [100x+10y+50+z]–50= 100x+10y+z


You are 15 years old, and you have 3 siblings.
The first two digits on the left (15) give your age, and the rightmost digit (3) gives the number of siblings you have. 


The algebraic equivalent of the steps result in Step 6, which is 100x + 10y + z, where z<10. But 100x + 10y + z is the algebraic equivalent of a three-digit number, with the digits in the hundreds and tens places giving the age, and the digit in the ones place giving the number of persons in the house. (Note: the number of siblings has to be less than 10, otherwise this “trick” will not work.)

Abir Basak

Having spent about two decades in the corporate arena, leading teams in IT across diverse industries, I decided to embark on a journey to contribute to the society using my knowledge and experience. A departure from the usual to bring together a new meaning to my career and life as a whole. After all, you can't set sail if you're scared to lose sight of the shore. Join in at

More Posts

Your Own Mathematics Puzzle was last modified: March 4th, 2016 by Abir Basak