If the simple interest on a certain sum of money for 7 years is one–fifth of the sum, then the rate of interest per annum is  Pick.
A) 4 % B) 2.50 % C) 6.20 % D) 5 % E) 2.85 %

Rationale: "explanation : let the principal ( p ) be x then , simple interest ( si ) = x / 5 time ( t ) = 7 years rate of interest per annum ( r ) = ( 100 × si ) / pt = ( 100 × ( x / 5 ) / ( x × 7 ) = 20 / 7 = 2.85 % answer : option e"
Answer: E