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) Rs. 12000; 12% p.a. B) Rs. 22000; 12% p.a. C) Rs. 12000; 22% p.a. D) Rs. 12000; 14% p.a. E) Rs. 12000; 16% p.a.
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.   Rs. 12000; 12% p.a.NSWER:Rs. 12000; 12% p.a.
<result>A</result>
A certain sum becomes Rs. 20720 in four years and 24080 in six years at simple interest. Find sum and rate of interest?