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?  Choices.
A) 50% B) 25% C) 10% D) 30% E) 18%
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 2rd year and 6th year = $200 - $100 = $100   As the simple interest earned for a period of 4 years is $ 100, interest earned per year 200 -  100= 
<gadget id="calculator">200 -  100</gadget>
<output>100</output>
$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= 
<gadget id="calculator">2 * 25</gadget>
<output>50</output>
$ 50.   Hence, initial amount invested X= Amount after 2years - interest for 2 years   = 100 - 50= 
<gadget id="calculator">100 - 50</gadget>
<output>50</output>
$ 50.   Rate of interest= (interest per year/principal)*100 = 25/50*100= 
<gadget id="calculator">25/50*100</gadget>
<output>50</output>
50%   correct choice is 50%
<result>A</result>
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?