Peter invested a certain sum of money in a simple interest bond whose value grew to $400 at the end of 4 years and to $ 500 at the end of another 2 years. What was the rate of interest in which he invested his sum?	Choose the correct choice from the following
A) 12 %	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 4 years the principal p amounts to $ 400 and after a time of 6 years ( question says after another 6 years so 4 + 2 ) p becomes $ 500 . formulating the above data amount ( a 1 ) at end of 4 years a 1 = p ( 1 + 4 r / 100 ) = 400 amount ( a 2 ) at end of 6 years a 2 = p ( 1 + 2 r / 100 ) = 500 dividing a 2 by a 1 we get ( 1 + 4 r / 100 ) / ( 1 + 2 r / 100 ) = 5 / 4 after cross multiplication we are left with 4 r = 100 which gives r = 25 % option : d"
Answer: D