A certain sum of money doubles itself in 5 years at simple interest. In how many years it becomes seven times?

A 10 years

B 20 years

C 30 years

D 32 years

E None of these

Correct Answer: Option C

For simple interest, We know the amount of interest = PRT/100

A certain sum of money doubles itself in 5 years at simple interest.

Hence, interest is same as the sum of money.

Hence, P=(P×R×5)/100

⇒ 5R =100

⇒ R = 20%

The money has to become 7 times, Interest will be 6 times.

Hence, 6P = P×20×t/100

⇒ 20t = 600

⇒ t = 30

Hence, it will become 7 times in 30 years.