### What is the difference between the simple interest on a principal of Rs. 500 being calculated at 5% per annum for 3 years and 4% per annum for 4 years?

A. Rs. 5 B. Rs. 10 C. Rs. 20 D. Rs. 40 Answer: Option A
\begin{aligned}I_1&=\frac{PT_1R_1}{100}\\ I_1&=\frac{500\times3\times5}{100}\\ &=Rs.75\\ I_2&=\frac{PT_2R_2}{100}\\ I_2&=\frac{500\times4\times4}{100}\\ &=Rs.80\\ \text{ Difference }&=80-75\\ &=\text{ Rs. }5\end{aligned}