If the simple interest on a certain sum of money for 4 years is one–fifth of the sum, then the rate of interest per annum is  Choose the correct choice from the following answers:
A) 4%
B) 7%
C) 6%
D) 5%
E) 3%
Explanation:   Let the Principal(P) be x   Then, Simple Interest(SI) = x/5   Time(T) = 4 years   Rate of interest per annum(R) = (100×SI)/PT   = (100 × (x/5)/(x × 4) = 20/4= 
<gadget id="calculator">20/4</gadget>
<output>5</output>
5%   Answer: Option 5%
<result>D</result>
If the simple interest on a certain sum of money for 4 years is one–fifth of the sum, then the rate of interest per annum is