If a sum of money doubles itself in 15 years at simple interest, the ratepercent per annum is Select the correct option.
A) 12
B) 12.5
C) 6.67
D) 13.5
E) 14

Rationale: "explanation : let sum = x then simple interest = x rate = ( 100 * x ) / ( x * 15 ) = 6.67 option c"
Answer: C