Unit prices are common ways of displaying the price in supermarkets. They tell you the cost per unit of quantity; this makes it easy to directly compare the price of two different items. For example, if you are comparing two different blocks of cheese (of different sizes) you can calculate the unit price per pound. This allows you to work out which is the cheaper of the two.
To calculate the unit price of an item, you need to find the cost and divide it by the quantity.
Let's say you have two bags of apples on sale. One bag of apples is 3lbs and costs $19.50. Another is 1.5 lbs and costs $10.50 (assume that there is no additional tax to work out).
To work out the unit price of the first bag, we divide the cost by the units. Therefore, we do:
19.50 (cost) / 3 (weight in units) = 6.5
Therefore, the unit price of the first bag is $6.50/lb.
To work out the second bag, we follow the same steps:
10.50 (cost) / 1.5 (weight in units) = 7
Therefore, the unit price of the second bag is $7.00/lb
This means that the first bag is actually cheaper per pound.