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 price of A and B, respectively?

Let the cost price of watch A = Rs. N
Then, cost price of watch B = Rs. (650 - N)
Now, selling price of watch A = (120 x N) / 100 = Rs. 6N/5
Also, selling price of watch B = (650 - N) x (75/100) = Rs. {3 x (650 - N)}/4
As, according to the question, two selling prices are equal.
∴ 6N/5 = {3 x (650 - N)}/4
⇒ 8N = 5 x (650 - N)
⇒ 8N + 5N = 5 x 650
⇒ 13N = 5 x 650
⇒ N = (5 x 650)/13 = 250
∴ Cost price of watch A = Rs. 250
and cost price of watch B = (650 - 250) = Rs. 400