At what rate percent per annum will a sum of money double in 2 years.
Choose the most appropriate option: A) 34 % B) 50 % C) 11.5 % D) 20 % E) 21.5 %

Rationale: "let principal = p , then , s . i . = p and time = 8 years rate = [ ( 100 x p ) / ( p x 2 ) ] % = 50 % per annum . answer : b"
Answer: B