Number of Fans and Tubelight

Count the number of fan and tube light

This is a unique puzzle that will help you to play a very funny mathematical game with your friends that will let you guess the number of fan and tube light at his home without being there. Every household has fan, tube –light and many other electronics appliances. This game will let you know about two of the appliances present at your friends’ house whether it be tube-light, fan, LCD or any other appliances. For the convenience of reader this game has been based here on fan and tube light.

Tell your friend to do the following calculation on his copy as instructed by you.

1. Multiply the number of fan at your home by 2

2. Add 4 to it

3. Multiply it by 5

4. Add the number of tube-light at home to the previous result.

5. Subtract 20 and tell the final result

The result which your friend will give you have two digits. The number at the ten’s place will be the number of fan at his house and the digit at the unit place will tell you the tube light at home.

Example:- Suppose there are 5 fans and 8 tube-lights in your friend’s house. Let’s see the calculation as instructed.

1. Multiply the number of fan at your home by 2 = 5 × 2 = 10

2. Add 4 to it = 10 + 4 = 14

3. Multiply it by 5 = 14 × 5 = 70

4. Add the number of tube-light at home to the previous result = 70 + 8 = 78

5. Subtract 20 and tell the final result = 78 -20 = 58

Once your friend tells you his final result you can instantly tell the number of fans and tube- light present in his home.
5 8
Number of fan Number of tube- light

How does this puzzle work?

We know that a two digit number with x at ten’s place and y at the unit place = 10x + y

If x represent the number of fan at home and y represents the number of tube- lights at home then you will get the final result = 10x + y.

Let’s see the trick behind this puzzle.

1. Multiply the number of fan at your home by 2 = 2x

2. Add 4 to it = 2x + 4

3. Multiply it by 5 = (2x + 4) × 5 = 10x + 20

4. Add the number of tube-light at home to the previous result = 10x + 20 + y

5. Subtract 20 and tell the final result = 10x + 20 + y – 20 = 10x + y


Rajesh Kumar Thakur
rkthakur1974@gmail.com