A sum of money at compound interest doubles itself in 15 years. It will become eight times of itself in-

Question: A sum of money at compound interest doubles itself in 15 years. It will become eight times of itself in-Solution: let the sum P 2P = P (1 + r)15⇒ (1 + r)15 = 2let, sum will 8 times in n years8P = P(1 + r)n⇒ 8 = (1 + r)n⇒ 23 = (1 + r)n⇒ ((1 + r)15)3 = (1 + r)n⇒ (1 + r)45 = (1 + r)n∴ n = 45 years