The least number of complete years in which a sum of money put out at 20% compound interest will be more than doubled is:

Solution (By Examveda Team)

$$\eqalign{ & P{\left( {1 + \frac{{20}}{{100}}} \right)^n} > 2P\,\,\, \Rightarrow \,\,\,{\left( {\frac{6}{5}} \right)^n} > 2 \cr & {\text{Now}},\left( {\frac{6}{5} \times \frac{6}{5} \times \frac{6}{5} \times \frac{6}{5}} \right) > 2 \cr & So,\,n = 4\,{\text{years}} \cr} $$