Sales taxes add a percentage to the price of a purchase while discounts decrease the purchase price by a specified percentage. Being able to calculate discounts and sales taxes will help you better budget for the true cost of items so that you do not end up spending more than you anticipated nor do you pass up an item because you thought you couldn't afford it.
Things You'll Need
 Calculator

Divide the sales tax rate by 100 to find the sales tax expressed as a decimal. For example, if the rate equals 4.9 percent, divide 4.9 by 100 to get 0.049.

Multiply the sales tax rate as a decimal by the amount of your purchase. For example, if your pretax purchase total equals $460, multiply $460 by 0.049 to find the sales tax equals $22.54.

Add the sales tax to the original price to find the final price of the item. Finishing this example, add $22.54 to $460 to find the total to be $482.54.
Discounts

Divide the discount percentage by 100 to calculate the discount as a decimal. For example, if you have a 19 percent discount, divide 19 by 100 to get 0.19.

Subtract the discount expressed as a decimal from 1 to find the portion of the price that remains after the discount. In this example, subtract 0.19 from 1 to find you will pay $0.81 per dollar of the original cost.

Multiply the Step 2 result by the original price to find the price after the discount. Finishing this example, if the original price equals $200, multiply $200 by 0.81 to find that the price after a 19 percent discount equals $162.
References
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