At which sum the simple interest at the rate of $$3\frac{3}{4}$$ % per annum will be Rs. 210 in $$2\frac{1}{3}$$ years?
a) Rs. 1580
b) Rs. 2400
c) Rs. 2800
d) None of these

Answer: b
Explanation:
$$\eqalign{ & {\text{S}}{\text{.I}}{\text{.}} = {\text{Rs}}{\text{. 210}} \cr & {\text{R}} = 3\frac{3}{4}\% = \frac{{15}}{4}\% \cr & {\text{T}} = {\text{2}}\frac{{\text{1}}}{{\text{3}}}{\text{years}} = \frac{7}{3}{\text{years}} \cr & {\text{Sum}} = {\text{Rs}}{\text{.}}\left( {\frac{{100 \times 210}}{{\frac{{15}}{4} \times \frac{7}{3}}}} \right) \cr & = {\text{Rs}}{\text{.}}\left( {\frac{{100 \times 210 \times 4 \times 3}}{{15 \times 7}}} \right) \cr & = {\text{Rs}}{\text{. }}2400 \cr} $$