what should be the rate of interest to become a sum five times of itself in 8 years?  Choose the correct choice from the following answers.
A) 50  B) 40  C) 30  D) 20  E) 10
let the sum x,after 8 years it should 5x.4x is the interest.   4x=x*r*8/100   r=4*100/8= 
<gadget id="calculator">4*100/8</gadget>
<output>50</output>
50%   answer 50
<result>A</result>
what should be the rate of interest to become a sum five times of itself in 8 years?