Unit pricing
The unit price of something is the price for a fixed amount (usually the price per 100g, price per ml or price for one bar etc.) It is used in supermarkets to help customers compare the price of different sized items. When comparing, it is very important to use the same units when calculating the unit price.
Unit price is calculated by dividing the price by the mass (or The volume of a three-dimensional shape is a measure of the amount of space or capacity it occupies, eg an average can of fizzy drink has a volume of 330 ml. or number of items etc).
Eg Unit price = \(\frac{\text{price}}{\text{mass}}\)
Example
Which packet of biscuits is better value for money?
- £1 for 400 g
- £1.90 for 1 kg
It is hard to decide which item is better value if they are different sizes.
Note: it is easier to work with pence in this case as it removes the decimal in £1.90.
400 g packet
Unit price = \(\frac{\text{price}}{\text{mass}}\)
Unit price = \(\frac{100}{400}\)
The small packet cost 0.25 pence per gram.
1 kg packet
Unit price = \(\frac{\text{price}}{\text{mass}}\)
The units must be the same for the prices to be compared. 1 kg = 1,000 g.
Unit price = \(\frac{190}{1,000}\)
The large packet cost 0.19 pence per gram.
The large packet is better value, since the unit price is lower.