Q. At some rate of simple interest, A lent Rs. 6000 to B for 2 years and Rs. 1500 to C for 4 years and received Rs. 900 as interest from both of them together. The rate of interest per annum was:
Answer: 5%
Notes: If rate of interest be R% p.a. then,
$latex S.I. = \frac{Principal\times Time\times Rate}{100}&s=1$
$latex \therefore \frac{6000\times 2\times R}{100}+\frac{1500\times 4\times R}{100}=900&s=1$
$latex =>120R+60R=900$
$latex =>180R=900$
$latex =>R=\frac{900}{180}=&s=1$ 5%
Hence option [A] is the right answer