In a certain time a sum becomes 4 times as the rate of 5% per annum. At what rate of simple interest the same sum becomes 8 times in the same duration?

A. 12 2\3%

B. 11 3\5%

C. 11 2\3%

D. 12 3\5%

Solution(By Examveda Team)

Let 100 was the Sum.

Amount = 400.

Interest = 300.

R = 5%.

Time = T (Let).

Interest = PTR/100 = (100 *T *5)/100.

500T /100 = 300

5T = 300

T = 60 years.

Now for second case,

Let rate = r.

Time = 60 years.

Amount = 800.

Interest = 700.

Now,

I = PTr/100

700 = 100*60 *r/100

60r = 700

r = 70/6 = 11.66%.