A sum of money invested at compound interest doubles itself in 20 years. In how many years will it become 4 times of itself? MCQ with Answer and Explanation

A sum of money invested at compound interest doubles itself in 20 years. In how many years will it become 4 times of itself?

A. 30 years

B. 50 years

C. 40 years

D. 60 years

Answer: Option C

The sum doubles (2^1) in 20 years. It will become 4 (2^2) times in 2 * 20 = 40 years.

This question belongs to: Maths Compound Interest

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Question #1 Report Error

The simple interest on a sum for 2 years at 6% is Rs. 360. The compound interest for the same period and rate is:

A. Rs. 372.00

B. Rs. 370.80

C. Rs. 378.00

D. Rs. 375.00

Correct Answer: Option B

Explanation:
P = 36000/(6×2) = 3000. CI = 3000[(1.06)² − 1] = 3000 × 0.1236 = Rs. 370.80.

This question belongs to: Maths Compound Interest

Question #2 Report Error

At what rate percent compound interest will a sum of money become 9 times in 2 years?

A. 250%

B. 150%

C. 100%

D. 200%

Correct Answer: Option D

Explanation:
(1 + r)² = 9 ⇒ 1 + r = 3 ⇒ r = 2 = 200%.

This question belongs to: Maths Compound Interest

Question #3 Report Error

In how many years will Rs. 800 amount to Rs. 968 at 10% per annum compound interest?

A. 1.5 years

B. 2.5 years

C. 2 years

D. 3 years

Correct Answer: Option C

Explanation:
800(1.1)^t = 968 ⇒ (1.1)^t = 1.21 = (1.1)² ⇒ t = 2.

This question belongs to: Maths Compound Interest