If a sum of money doubles itself in 25 years at simple interest, the ratepercent per annum is
Pick one:
A) 12
B) 12.5
C) 13
D) 13.5
E) 4

Rationale: "explanation : let sum = x then simple interest = x rate = ( 100 * x ) / ( x * 25 ) = 4 option e"
Answer: E