At what rate percent on simple interest will a sum of money double itself in 40 years?	Choose the correct option.
A) 3 1/3%	B) 2 1/2%	C) 3 9/3%	D) 3 2/3%	E) 3 6/3%
P = (P*40*R)/100   R = 2 1/2%   Answer: 2 1/2%
<result>B</result>
At what rate percent on simple interest will a sum of money double itself in 40 years?