The bankers discount on Rs. 1800 at 12% per annum is equal to the true discount on Rs 1872 for the same time at the same rate. Find the time.

Answer: Option A

S.I. on Rs. 1800 = T.D. on Rs. 1872
P.W. of Rs. 1872 is Rs. 1800
Rs. 72 is S.I. on Rs. 1800 at 12%
$$\begin{array}{rl}& \text{Time}=\frac{100\times 72}{12\times 1800}\\ & =\frac{1}{3}\text{years}\\ & =4\text{months}\end{array}$$