A sum of money triples itself in 3 years at compound interest. In how many years will it become 9 times? MCQ with Answer and Explanation

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A sum of money triples itself in 3 years at compound interest. In how many years will it become 9 times?

A. 5 years

B. 8 years

C. 6 years

D. 7 years

Answer: Option C

Solution (By JKSSB Mock Tests)

3 times in 3 years; 9 = 3², so time = 3 × 2 = 6 years.

This question belongs to: Maths Compound Interest

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Question #1

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What is the compound interest on Rs. 80000 for 1 year at 10% per annum, compounded half-yearly?

A. Rs. 8200

B. Rs. 8000

C. Rs. 8600

D. Rs. 8400

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Correct Answer: Option A

Explanation:
Half-yearly rate = 10/2 = 5%. Time = 2 half-years. Amount = 80000 * (1 + 5/100)^2 = 80000 * 1.1225 = Rs. 88200. Compound Interest = 88200 - 80000 = Rs. 8200.

This question belongs to: Maths Compound Interest

Question #2

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The population of a small community grows by 10% in the first year and decreases by 10% in the second year. If the population at the end of 2 years is 39600, find the original population.

A. Rs. 44000

B. Rs. 38000

C. Rs. 40000

D. Rs. 42000

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Correct Answer: Option C

Explanation:
Net change over 2 years = +10 - 10 - (1010)/100 = -1% (decrease). So, 99% of original population = 39600 => Original population = 39600 / 0.99 = 40000.

This question belongs to: Maths Compound Interest