The compound interest on Rs.2800 for 18 months at 10% p.a is = ?

Answer: Option B

$$\begin{array}{rl}& \text{Given,}\text{Principal},P=Rs.2800\\ & \text{Compound}\text{rate},R=10\%\text{per}\text{annum}\\ & =\frac{10}{2}=5\%\text{half - yearly}\\ & \text{Amount}\\ & =\text{Rs}\text{.}\left[2800\times \left(1+\frac{10}{100}\right)\left(1+\frac{5}{100}\right)\right]\\ & =\text{Rs.}\left(2800\times \frac{11}{10}\times \frac{21}{20}\right)\\ & =\text{Rs. }3234\\ & \therefore \text{C}\text{.I}\text{. = Rs.}\left(3234-2800\right)\\ & =\text{Rs. }434\end{array}$$