Multiple choice

The difefrence between the compound interest on a certain sum for the second year and the third year at 5% p.a. is Rs.42. Find the sum. एक निश्चित धनराशि पर 5% वार्षिक ब्याज की दर से दूसरे वर्ष के चक्रवृद्धि ब्याज और तीसरे वर्ष के चक्रवृद्धि ब्याज में अन्तर 42 रु. है | धनराशी ज्ञात कीजिये |

  1. Rs./रु.12000

  2. Rs./रु.15000

  3. Rs./रु.16000

  4. Rs./रु.20000
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C Correct answer
Explanation

CI for 2nd year = P(1.05)² - P(1.05) = P×0.05×1.05. CI for 3rd year = P(1.05)³ - P(1.05)² = P×0.05×(1.05)². Difference = P×0.05×1.05×0.05 = 42. Solving gives P = 16000. The difference between consecutive years' compound interest is the interest on the previous year's interest.

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