Multiple choice

If the ratio of difference of compound interest and simple interest for same rate of interest after two years to that of after three years is 4 : 15, then find the rate of interest. यदि 2 वर्षों में चक्रवृद्धि ब्याज और साधारण ब्याज के अन्तर और उसी दर से 3 वर्षों के चक्रवृद्धि ब्याज और साधारण ब्याज के अन्तर का अनुपात 4 : 15 हो तो ब्याज की दर ज्ञात कीजिये |

  1. 25%

  2. 50%

  3. 75%

  4. 5%
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C Correct answer
Explanation

For compound and simple interest, the difference after n years is CI - SI = P(r/100)² for n=2, and = P(r/100)²(3 + r/100) for n=3. Ratio = P(r/100)² : P(r/100)²(3 + r/100) = 1 : (3 + r/100) = 4 : 15. Solving 3 + r/100 = 15/4 gives r/100 = 3/4, so r = 75%.

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