If the simple interest on a certain sum of money for 5 years is one–fifth of the sum, then the rate of interest per annum is Choose the correct choice from the following:
A) 4 %	B) 7 %	C) 6 %	D) 4 %	E) 3 %

Rationale: "explanation : let the principal ( p ) be x then , simple interest ( si ) = x / 5 time ( t ) = 5 years rate of interest per annum ( r ) = ( 100 × si ) / pt = ( 100 × ( x / 5 ) / ( x × 5 ) = 20 / 5 = 4 % answer : option d"
Answer: D