The least number of complete years, in which a sum of money put at 20% compound interest will be more than doubled, is :20% चक्रवृद्धि ब्याज पर एक धनराशि न्यूनतम कितने पूर्ण वर्षों में दुगुना से अधिक हो जायेगी ?

1. A2
2. B3
3. C4
4. D5

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Correct answer: C. 4

Explanation

We need (1.2)ⁿ > 2. Now (1.2)² = 1.44, (1.2)³ = 1.728 and (1.2)⁴ = 2.0736. The amount first exceeds double in the 4th year.हमें (1.2)ⁿ > 2 चाहिए। (1.2)² = 1.44, (1.2)³ = 1.728 तथा (1.2)⁴ = 2.0736। अतः राशि पहली बार 4 वर्षों में दुगुने से अधिक होती है।