What is the <strong>LEAST</strong> number of complete years in which a sum of money put out at 20% compound interest (compounded annually) will be more than doubled ?

Explanation

We need the amount P(1+0.20)^n \gt 2P, which means 1.2^n \gt 2. Computing powers of 1.2: 1.2^2 = 1.44, 1.2^3 = 1.728, 1.2^4 = 2.0736. The least number of complete years is 4.

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