Multiple choice

A sum borrowed under compounded interest doubles itself in 10 years when will it become fourfold of itself at the same rate of interest ? चक्रवृद्धि व्याज के अंतर्गत उधार ली गयी एक धनराशि 10 वर्षो में दुगनी हो जाती है| वह राशि उसी ब्याज की दर से कितने समय में अपने से चार गुनी हो जायेगी?

  1. 15 years/ वर्ष

  2. 20 years/ वर्ष

  3. 24 years/ वर्ष

  4. 25 years/ वर्ष
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Let P be principal and r be rate. P(1+r)¹⁰ = 2P, so (1+r)¹⁰ = 2. For amount to become 4P: P(1+r)ⁿ = 4P = 2²P = [(1+r)¹⁰]²P = (1+r)²⁰P. Thus n = 20 years. Option B is correct.

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