A sum at simple interest becomes two times in 8 years at a certain rate of interest p.a. The time in which the same sum will be 4 times at the same rate of interest at simple interest is:

24 years 

A sum at simple interest becomes two times in 8 years at a certain rate of interest p.a.

Let principal = P

So , Amount = 2p  in 8 years

SI = Amount - Principal

= 2P - P

= P

We know ,

Simple Interest = \(\frac{Principal ×Rate × Time }{100}\)

P = \(\frac{P×Rate × 8 }{100}\)

Rate = 12.5%

Now, Required amount is 4 times of Initial Sum.

3P = \(\frac{P× 12.5 ×Time }{100}\)

Time = 24  years