# What will be the Natural Number? If

The average of some natural numbers is 15. If 30 is added to first number and 5 is subtracted from the last number the average becomes 17.5 then the number of natural number is:

- 20
- 30
- 15
- 10

**Answer: (4) 10**

**Explanation:-**

Let be the number of natural number is X

The average X natural number = 15

The sum of X natural number = 15 x X = 15X

30 is added to first number and 5 is subtracted from the last number.

Then, the sum of X natural number = 15X + 30 – 5 = 15X + 25

Then, average = (15X + 25 ) /X = 17.5

= 15X + 25 = 17.5X

2.5X = 25

X = 10

Hence, the number of natural number is 10.