Markup refers to the amount that a good's price is increased above its cost when it is sold. For example, a retailer may pay $100 for a sweater but then mark it up 30 percent so the cost to the customer is actually $130. The higher the markup the larger the profit for the retailer. However, if markups are too high, the customers may seek other retailers to purchase from. If you know the markup percentage and cost, you can find the sales price.

Divide 20 percent by 100 to get find that 20 percent expressed as a decimal equals 0.2.

Multiply the markup of 0.2 by the cost of the item. For example, if the item costs $30, you would multiply $30 by 0.2 to get $6.

Add the markup to the cost of the item to find the selling price of the item. In this example, you would add the markup of $6 to the $30 cost to find a selling price of $36.