In what time will Rs. 1860 amount to 2641.20 at simple interest 12% per annum ?

Answer: Option B

$$\begin{array}{rl}& \text{Rate }\%=\text{12}\%\\ & \text{Principal = Rs}\text{. 1860}\\ & \text{Amount = Rs}\text{. 2641}\text{.20}\\ & \text{Interest}\\ & \text{ = Rs}\text{. }\left(2641.20-1860\right)\\ & =\text{Rs}\text{. 781}\text{.20}\\ & \text{By using formula,}\\ & \text{Required time }\\ & =\frac{781.20\times 100}{1860\times 12}\\ & =3\frac{1}{2}\text{ years}\end{array}$$