The simple interest on a certain sum of money at the rate of 5% p.a. for 8 years is Rs. 840.At what rate of interest the same amount of interest can be received on the same sum after 5 years ?  Choose the correct choice from the following options
A) 6%
B) 8%
C) 9%
D) 10%
E) None
Solution   S.I. = Rs. 840,R =5%,T= 8 Years.   Principal = Rs.(800x840/5x8)= Rs. 2100.   Now,P = Rs. 2100,S.I. = Rs. 840, T = 5 years.   ∴ Rate =(100x840/2100x5) = 8%.   Answer 8%
<result>B</result>
The simple interest on a certain sum of money at the rate of 5% p.a. for 8 years is Rs. 840.At what rate of interest the same amount of interest can be received on the same sum after 5 years ?