A sum of money placed at C.I. interest doubles itself in 5 years. It will amount to eight times itself at the same rate of interest in?

A. 7 years
B. 10 years
C. 15 years
D. 20 years

Explanation:

P(1 + R/100)⁵ = 2P => (1 + R/100)⁵ = 2

Let P(1 + R/100)ⁿ = 8P
=> (1 + R/100)ⁿ = 8 = 23 = {(1 + R/100)⁵}³
=> (1 + R/100)ⁿ = (1 + R/100)¹⁵ => n = 15 Required time = 15 years.

Correct Answer: 15 years ✔

Last Updated: February 07, 2020