Multiple choice

A sum of money at compound interest double itself in 13 years. It will become eight times of itself in एक राशि चक्रवृद्धि ब्याज पर 13 वर्ष में अपने आप की दुगनी हो जाती है। यह अपने की आठ गुनी हो जाएगी:

  1. 45 years 45 साल

  2. 48 years 48 साल

  3. 54 years 54 साल

  4. 60 years 60 साल

  5. 39 years 39 साल
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E Correct answer
Explanation

If amount doubles in 13 years, then 2P = P(1 + r)^13, so (1 + r)^13 = 2. To become 8 times: 8P = P(1 + r)^n, so (1 + r)^n = 8 = 2^3. Since (1 + r)^13 = 2, we need (1 + r)^(13×3) = 2^3, so n = 13 × 3 = 39 years.

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