# Find Out the First Number.

The average of three numbers is 21. If the first number is double of the second number and the second number is double of the third number, find out the first number.

- 30
- 60
- 35
- 36

**Answer: (4) 36**

**Explanation:-**

The average of three numbers = 21

Then, the sum of three numbers = 21 x 3 = 63

Let the second number be X, first number 2 X & third number is X/2.

Then, 2 X + X + X/2 = 63

( 2 x 2 X + 2 x X + X)/2 = 63

4 X + 2 X + X = 63 x 2

7 X = 126

X = 126/7

X = 18

Then, the first number is 2 X = 2 x 18 = 36.

Hence, the answer is (4) 36.