How to solve profit loss sums quickly?

Whenever a problem on profit loss is given, identify the data regarding cost price, selling price, marked price, discount and profit/loss quickly. If the data of any of the above terms is not given, then try to find its value using the information of the other terms. Have these 4 formulae on your tips and practice a lot:
1) Profit/Loss = Selling Price - Cost Price
2) Profit/Loss % = $$\frac{Profit/Loss}{Cost Price} * 100$$
3) Marked Price - Discount = Selling Price
4) Selling Price = Marked Price ($$1-\frac{Discount}{100}$$)