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

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

A. 6 years

B. 10 years

C. 8 years

D. 7 years

Answer: Option C

Solution (By JKSSB Mock Tests)

81 = 9², so 4 × 2 = 8 years.

This question belongs to: Maths Compound Interest

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Question #1

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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?

A. 40 years

B. 50 years

C. 20 years

D. 30 years

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Correct Answer: Option D

Explanation:
The sum becomes 2^1 times in 10 years. It will become 8 (2^3) times in 3 * 10 = 30 years.

This question belongs to: Maths Compound Interest

Question #2

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At what rate of compound interest per annum will a sum of Rs. 800 become Rs. 882 in 2 years?

A. 8%

B. 4%

C. 5%

D. 6%

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Correct Answer: Option C

Explanation:
800 × (1 + r)² = 882 ⇒ (1+r)² = 1.1025 ⇒ 1+r = 1.05 ⇒ r = 5%.

This question belongs to: Maths Compound Interest

Question #3

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A sum of money placed at compound interest becomes double of itself in 5 years. In how many years will it become 128 times of itself?

A. 40 years

B. 45 years

C. 35 years

D. 30 years

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Correct Answer: Option C

Explanation:
The sum becomes 2^1 times in 5 years. It will become 128 (2^7) times in 7 * 5 = 35 years.

This question belongs to: Maths Compound Interest

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