Peter invested a certain sum of money in a simple interest bond whose value grew to $100 at the end of 2 years and further to $200 at the end of another 4 years. What was the rate of interest in which he invested his sum?  Select
A) 50 % B) 25 % C) 10 % D) 30 % E) 18 %

Rationale: "explanatory answer initial amount invested = $ x amount at the end of year 2 = $ 100 amount at the end of year 6 ( another 4 years ) = $ 200 therefore , the interest earned for the 4 year period between the 2 rd year and 6 th year = $ 200 - $ 100 = $ 100 as the simple interest earned for a period of 4 years is $ 100 , interest earned per year = $ 25 . therefore , interest earned for 2 years = 2 * 25 = $ 50 . hence , initial amount invested x = amount after 2 years - interest for 2 years = 100 - 50 = $ 50 . rate of interest = ( interest per year / principal ) * 100 = 25 / 50 * 100 = 50 % correct choice is a"
Answer: A