The C.P. of two watches taken together is Rs. 840. If by selling one at a profit of 16% and the other at a loss of 12% , there is no loss or gain in the whole transaction, then the C.P. of the two watches are respectively.

Explanation:-

C.P. = Cost Price.
Let the C.P. of the watches be Rs. x and Rs. (840 - x)
∴ (116% of x) + [88% of (840 - x)] = 840
⇒ 116x + 73920 - 88x = 84000
⇒ 28x = 10080
⇒ x = 360
∴ Their cost prices are Rs. 360 and Rs. 480