The least number of complete years in which a sum of money put out at 20\% compound interest will be more than doubled is
(a)3
(b)4
(c)5
(d)6
Answer
Answer (as printed): B
Explanation
$P\left(1+\frac{20}{100}\right)^{n}>2 P$ or $\left(\frac{6}{5}\right)^{n}>2$. Now, $\left(\frac{6}{5} \times \frac{6}{5} \times \frac{6}{5} \times \frac{6}{5}\right)>2$. So, $n=4$ years.
Explanation as extracted from the printed page; notation may be imperfect.