In how many years will a sum of money doubles itself at 5% per annum simple interest	Choose the correct choice
A) 25 years B) 28 years C) 10 years D) 20 years E) 21 years

Rationale: "let the initial sum be x then , amount = 2 x ( because sum will be double ) amount = principal + s . i 2 x = x + s . i s . i = x s . i = ( p * r * t ) / 100 x = ( x * 5 * t ) / 100 therefore , t = 20 years answer : d"
Answer: D