A bookseller sells a book at a profit of 10% . If he had bought it at 4% less and sold it for Rs. 6 more, he would have gained 183/4 %. The cost price of the book is -

Answer: Option C

Let C.P. of the book be Rs. 100
Profit = 10%. S.P. = Rs. 110
New C.P. = 4% less = Rs. 96
If gain is $$18\frac{3}{4}\%$$
$$\begin{array}{rl}& \text{Then S}\text{.P}\text{.}\\ & =\left(118\frac{3}{4}\%\text{ of Rs}\text{. }96\right)\\ & =\text{Rs}.\left(\frac{475}{4}\times \frac{1}{100}\times 96\right)\\ & =\text{Rs}\text{. }114\end{array}$$
Difference in S.P. = Rs. (114 - 110) = Rs. 4
If difference in S.P. is Rs. 4, C.P. = Rs. 100
If difference in S.P. is Rs. 6,
$$\begin{array}{rl}& \text{C}\text{.P}\text{.}=\text{Rs}\text{.}\left(\frac{100}{4}\times 6\right)\\ & =\text{Rs}\text{. }150\end{array}$$