A certain sum becomes Rs. 20720 in four years and 24080 in six years at simple interest. Find sum and rate of interest?
Choices.
A) 11
B) 12
C) 44
D) 66
E) 81
:   Let the interest for one year be x.   As amount = Principal + Interest, we have   P + 4x = 20720 --- (1) ; P + 6x = 24080 --- (2)   Solving the equations (1) and (2), we can get   P = Rs. 14000 and x = Rs. 1680   Interest for one year on Rs. 14000 is Rs. 1680   So, R = (100 * 1680)/(14000 * 1)= 
<gadget id="calculator">(100 * 1680)/(14000 * 1)</gadget>
<output>12</output>
12% p.a.Answer: 12
<result>B</result>
A certain sum becomes Rs. 20720 in four years and 24080 in six years at simple interest. Find sum and rate of interest?