Simple & Compound Interest

JKSSB Junior Engineer (Mechanical) · Mathematics · 49 practice questions with answers and explanations: 21 Easy, 27 Medium, 1 Hard.

Sample questions

Sample Easy question 1

At what rate of simple interest per annum will Rs. 12000 amount to Rs. 14400 in 4 years?

  1. 4%
  2. 5%
  3. 7%
  4. 6%
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Answer: B. Simple interest = 14400 − 12000 = Rs. 2400. Rate = (2400 × 100) ÷ (12000 × 4) = 5%.

Sample Easy question 2

At what rate of simple interest per annum will Rs. 8000 amount to Rs. 8960 in 2 years?

  1. 6%
  2. 8%
  3. 7%
  4. 5%
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Answer: A. Simple interest = 8960 − 8000 = Rs. 960. Rate = (960 × 100) ÷ (8000 × 2) = 6%.

Sample Easy question 3

At what rate of simple interest per annum will Rs. 12000 amount to Rs. 15000 in 5 years?

  1. 5%
  2. 4%
  3. 6%
  4. 7%
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Answer: A. Simple interest = 15000 − 12000 = Rs. 3000. Rate = (3000 × 100) ÷ (12000 × 5) = 5%.

Sample Medium question 4

A sum of Rs. 8000 becomes Rs. 9261 in 3 years at compound interest, compounded annually. Find the rate of interest.

  1. 7%
  2. 4%
  3. 5%
  4. 6%
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Answer: C. 9261/8000 = (1+r/100)³. Taking the cube root: 1+r/100 = 1.05, so r = 5%.

Sample Medium question 5

The compound interest on a sum for 2 years is Rs. 832, and the simple interest for the same period at the same rate is Rs. 800. Find the rate of interest.

  1. 7%
  2. 6%
  3. 8%
  4. 9%
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Answer: C. The difference (832-800=32) equals SI×(R/200) for 2 years, since CI-SI = SI×R/200 when SI is for the same period: 32 = 800×R/200, giving R = 8%.

Sample Medium question 6

A sum of money invested at compound interest amounts to Rs. 4840 in 2 years and Rs. 5324 in 3 years. Find the rate of interest.

  1. 10%
  2. 12%
  3. 9%
  4. 8%
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Answer: A. The interest earned in the 3rd year = 5324-4840 = 484, which is the interest on Rs. 4840 for 1 year. Rate = (484×100)/4840 = 10%.

Sample Hard question 7

Find the compound interest on Rs. 10,000 for 1.5 years at 10% per annum, compounded half-yearly.

  1. 1600
  2. 1576.25
  3. 1500
  4. 1550
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Answer: B. With 5% per half-year over 3 periods, amount = 10000 × 1.05³ ≈ 11576.25, so CI ≈ 1576.25.

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