An amount at compound interest sums to Rs.17640/- in 2 years and to Rs.20286/- in 3 years at the same rate of interest. Find the rate percentage?  Choose the correct option.
A) 5%  B) 7%  C) 9%  D) 15%  E) 12%
Explanation:   The difference of two successive amounts must be the simple interest in 1 year on the lower amount of money.   S.I = 20286/- - 17640/- = Rs. 2646/-   Rate of interest = (2646/17640) × (100/1) =&gt; 15%   Answer: Option 15%
<result>D</result>
An amount at compound interest sums to Rs.17640/- in 2 years and to Rs.20286/- in 3 years at the same rate of interest. Find the rate percentage?