Multiple choice

A sum of money placed at compound interest doubles itself in 5 years. It will amount to eight times of itself at the same rate of interest in- एक निश्चित धनराशि चक्रवृद्धि ब्याज से 5 वर्ष में दोगुनी हो जाती है। यह स्वयं का आठ गुना उसी ब्याज की दर से कितने समय में हो जायेगी-

  1. 10 years/वर्ष

  2. 12 years/वर्ष

  3. 15 years/वर्ष

  4. 20 years/वर्ष
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

If money doubles in 5 years at compound interest, then (1+r)^5 = 2. For eight times: (1+r)^n = 8 = 2^3 = ((1+r)^5)^3 = (1+r)^15. Therefore n = 15 years. The money will become eight times itself in 15 years at the same compound interest rate.

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