A merchant sold an article at 10% loss. If he had sold it Rs 450 more, 8% would have been gained on the cost price. Find the cost price ?

Let the cost price be 100%. It is sold at 10% loss. So it is sold at 90% of the cost price.
90 % of the cost price + 450 = 108% of the Cost price.
18% of the cost price = Rs.450
Cost price of the book = 450/18 x 100
= Rs 2500 .