At what rate percent per annum will a sum of money double in 10years?  Choose the correct choice from the following answers:
A) 10 %	B) 15 %	C) 18 %	D) 20 %	E) 25 %

Rationale: "let principle = p s . i . = p t = 10 yrs rate = 100 * p / p * 10 = 10 % answer is a"
Answer: A