A sum of money placed at compound interest becomes double of itself in 10 years. In how many years will it become 8 times of itself? MCQ with Answer and Explanation

Explanation:
Effective rate of compound interest for 2 years at 5% = 5 + 5 + (55)/100 = 10.25%. Given 10.25% of P = 205 => P = 205 / 0.1025 = Rs. 2000.

Explanation:
Half-yearly rate = 10/2 = 5%. Time = 1.5 years = 3 half-years. Amount = 16000 * (1 + 5/100)^3 = 16000 * (1.05)^3 = 16000 * 1.157625 = Rs. 18522. Compound Interest = 18522 - 16000 = Rs. 2522.

Explanation:
(1 + r)² = 1.21 ⇒ 1 + r = 1.1 ⇒ r = 10%.