Consumer Mathematics: Financial Management
How to Compare prices to find the best buy
Use this to decide which of several offers gives the best value for money.
Before you start
- Dividing money by a quantity
- Working out a percentage discount
- Comparing decimals to see which is smaller
- Keeping the same units for each offer
When to use it
Use this to decide which of several offers gives the best value for money.
The steps
- Work out the price per unit (per gram, per item) for each offer.
- Divide the price by the quantity to get the unit price.
- Compare the unit prices, not the total prices.
- Account for any discount or bundle in the unit price.
- Choose the lowest unit price and state it clearly.
Worked example
A shop sells rice two ways: Offer A is 2 kg for RM11.00, and Offer B is 5 kg for RM26.50. Which offer is the best buy?
- Work out the price per kilogram for each offer.
- Offer A: RM11.00 ÷ 2 kg = RM5.50 per kg.
- Offer B: RM26.50 ÷ 5 kg = RM5.30 per kg.
- Compare the unit prices, not the totals: RM5.30 < RM5.50 (there is no discount here to adjust).
- Choose the lowest unit price: Offer B at RM5.30 per kg.
A second example, with a twist
One offer is a bundle with a percentage discount, so you must apply the discount before working out the unit price. Two juice offers: Offer X is 3 bottles for RM12.00.
Offer Y is 4 bottles at RM4.20 each, with 10% off the total for buying four. Which offer is the best buy?
- Work out the price per bottle for each offer.
- Offer X: RM12.00 ÷ 3 = RM4.00 per bottle.
- Offer Y before discount: 4 × RM4.20 = RM16.80.
- Account for the bundle discount: 10% off means paying 90%, so RM16.80 × 0.90 = RM15.12; per bottle = RM15.12 ÷ 4 = RM3.78.
- Compare the unit prices: RM3.78 < RM4.00, so choose Offer Y at RM3.78 per bottle.
Formulae you may need
Formula pages
Practise this in a KBAT problem
Frequently asked questions
Why compare the unit price instead of the total price?
The offers usually cover different quantities, so the totals are not a fair comparison. The price per unit puts every offer on the same footing, so you can see which one truly costs less for the same amount.
The bigger pack costs more overall, so how can it be cheaper?
It costs more in total because it contains more, but the price for each unit can still be lower. Best buy is about value per unit, not the total on the price tag, so always divide before you decide.
How do I handle a discount like '10% off'?
Work out what fraction you actually pay: 10% off means you pay 90%, so multiply the price by 0.90. Do this before dividing by the quantity, so the discount is included in the unit price you compare.