A sum of money invested at compound interest doubles itself in 7 years. In how many years will it become 8 times of itself? MCQ with Answer and Explanation

Question

A sum of money invested at compound interest doubles itself in 7 years. In how many years will it become 8 times of itself?

A. 28 years

B. 14 years

C. 21 years

D. 35 years

Answer: Option C

Solution (By JKSSB Mock Tests)

The sum doubles (2^1) in 7 years. It will become 8 (2^3) times in 3 * 7 = 21 years.

This question belongs to: Maths Compound Interest

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Question #1

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At what rate percent per annum will Rs. 32000 amount to Rs. 37232 in 3 years, compound interest compounded annually?

A. 5%

B. 8%

C. 6%

D. 4%

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Correct Answer: Option A

Explanation:
Amount/Principal = 37232 / 32000 = 4654 / 4000 = 9261 / 8000 = (21 / 20)^3. Therefore, 1 + R/100 = 21/20 => R/100 = 1/20 => R = 5%.

This question belongs to: Maths Compound Interest

Question #2

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The compound interest on a sum for 2 years at 4% is Rs. 408. The sum is:

A. Rs. 5400

B. Rs. 4800

C. Rs. 5200

D. Rs. 5000

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Correct Answer: Option D

Explanation:
CI = P[(1.04)² − 1] = P × 0.0816 = 408 ⇒ P = 5000.

This question belongs to: Maths Compound Interest

Question #3

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The difference between CI and SI on Rs. 12000 for 2 years at 5% is:

A. Rs. 25

B. Rs. 35

C. Rs. 30

D. Rs. 40

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Correct Answer: Option C

Explanation:
Difference = 12000 × (0.05)² = 12000 × 0.0025 = Rs. 30.

This question belongs to: Maths Compound Interest

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