A trader purchases a watch and a wall clock for Rs. 390. He sells them making a profit of 10% on the watch and 15% on the wall clock. He earns a profit of Rs. 51.50. The difference between the original prices of the wall clock and the watch is equal to
Let the cost of the watch = Rs. x.
Then, cost of the clock = Rs. (390−x)
Given, 10% of x+15% of (390−x)=51.50
⇒x10+15×(390−x)100=51.50
⇒10x+5850−15x=5150
⇒5x=700
⇒x=140
∴ Cost of clock = Rs. (390−140)= Rs. 250
∴ Required difference = Rs. 250−Rs. 140=Rs. 110.