Peter invested a certain sum of money in a simple interest bond whose value grew to $400 at the end of 3 years and to $ 600 at the end of another 2 years. What was the rate of interest in which he invested his sum?
Select the correct option.
A) 100 %
B) 12.5 %
C) 67 %
D) 25 %
E) 33 %

Rationale: "lets assume the principal amount ( initial amount invested ) to be p rate of interest to berand time as t . we need to find r now after a time of 3 years the principal p amounts to $ 400 and after a time of 5 years ( question says after another 5 years so 3 + 2 ) p becomes $ 600 . formulating the above data amount ( a 1 ) at end of 3 years a 1 = p ( 1 + 3 r / 100 ) = 400 amount ( a 2 ) at end of 8 years a 2 = p ( 1 + 5 r / 100 ) = 600 dividing a 2 by a 1 we get ( 1 + 5 r / 100 ) / ( 1 + 3 r / 100 ) = 6 / 8 after cross multiplication we are left with r = 100 option : a"
Answer: A