121.
The least number of complete years in which a sum of money put out at 20% compound interest will be more than doubled is:
Answer: B
The money more than doubles once \( (1.2)^{n} > 2 \). Test successive powers:
\[ (1.2)^{1} = 1.2, \qquad (1.2)^{2} = 1.44 \]
\[ (1.2)^{3} = 1.728, \qquad (1.2)^{4} = 2.0736 \]
The third year falls short and the fourth passes 2, so the answer is 4 years.
The question asks for complete years, so the answer must be a whole number even though the exact doubling time is about 3.8 years.
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