The rate at which a sum becomes four times of itself in 15 years at S.I., will be:

20%

20%

Solution:

Formula: Simple Interest,S.I = P n r /100 where,

P is the principal amount

n is the time duration in years and

r is the rate of interest in percentage.

It's given that, a certain sum of money becomes 4 times itself in 15 years.

So, Principal = x , Amount = 4x

S.I = 4x - x = 3x

By substitution in the formula we get,

3x = (x × 15 × r)/100

3 = (15 × r)/100

300 = 15 × r

r = 300/15

r = 20%

So, the correct option is D). 20%