A man purchases two clocks A and B at a total cost of Rs. 650. He sells A with 20% profit and B at a loss of 25% and gets the same selling price for both the clocks. What are the purchasing prices of A and B respectively ?

Let C.P. of clock A be Rs. x and that of clock B be Rs. (650 - x).
Then,
120% of x = 75% of (650 - x)
$$\eqalign{ & \Rightarrow 650 - x = \frac{{120}}{{75}}x \cr & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = \frac{8}{5}x \cr & \Rightarrow \frac{{13}}{5}x = 650 \cr & \Rightarrow x = \left( {\frac{{650 \times 5}}{{13}}} \right) \cr & \,\,\,\,\,\,\,\,\,\,\,\,\, = 250 \cr & \therefore {\text{C}}{\text{.P}}{\text{. of A}} = {\text{Rs}}{\text{. }}250 \cr & {\text{C}}{\text{.P}}{\text{. of B}} = {\text{Rs}}{\text{. }}400 \cr} $$