a deduction of the cost of an item

the price of an item after a discount

a certificate, either paper or electronic, that discounts an item by a set dollar amount of percentage

a coupon redeemable only if certain conditions are met, such as buying multiple of the same item, a certain size, et cetera

an amount of money added to the cost of an item based on a state's sales tax

the amount of money owed for the purchase of an item before tax and tip, if applicable

the amount of money added to the purchase of a meal, usually 20%

the amount of money added to the purchase of a meal, usually a minimum set by the establishment

the percent difference between a new value and an old value, calculated by subtracting the old value from the new value, then dividing by the old value

the percent that a number has increased, calculated as positive percent change

the percent that a number has increased, calculated as negative percent change

$$a+b=b+a$$  or $$\left(a\right)\left(b\right)=\left(b\right)\left(a\right)$$  

the price for one unit measurement, such as ounce, pound, gallon, et cetera

the formula for calculating unit price, calculated as the total cost of an item divided by the number of units in the item

a good buy, a discount over another similar item

the number of miles driven dived by the number of gallons of gas burned

the instrument in a car that measures miles driven

the number of miles driven on a gallon of gas