A sum of money at compound interest becomes 9 times in 4 years. In how many years will it become 81 times? MCQ with Answer and Explanation

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:
Quarterly rate = 3%, (1.03)⁴ = 1.12550881, effective ≈ 12.55%.

Explanation:
P = 9261 / 1.1025 = 8400.