GCSE MATHS • HIGHER TIER
Best Buys Made Simple
Compare products fairly by converting units and calculating cost per unit to find the best value for money.
Clear method
Exam practice
Worked proofs
Best Buys in Four Moves
1
Identify
Identify the products, prices and quantities being compared.
2
Convert
Convert measurements into the same units where necessary.
3
Calculate
Calculate the cost per unit for each option.
4
Compare
Choose the option with the lower cost per unit, or state if the value is the same.
What You’ll Learn
Understand Best Buys
Know how best-buy questions test value for money.
Calculate Unit Cost
Divide price by quantity to compare products fairly.
Convert Units
Use common conversions such as kilograms to grams and litres to millilitres.
Compare Offers
Recognise the lower unit cost as the better value.
Apply the Skill
Use best-buy calculations in shopping, contracts, subscriptions and budgeting.
Key Rules
Use the Same Units
Convert all quantities into the same unit before comparing.
Calculate Unit Cost
Divide the price by the quantity.
Compare Like for Like
Use the same unit cost, such as cost per gram, litre or item.
Lower Cost Means Better Value
The option with the lower cost per unit is the better buy.
Worked Proof: Best Buys
Step-by-Step Method
- 1. Identify the products being compared.
- 2. Convert measurements into the same units if necessary.
- 3. Calculate the cost per unit.
- 4. Compare the answers.
- 5. Choose the option with the lower cost per unit.
More Worked Examples
1
Question : Which is the better buy? 500g of rice costs £1.20. 1kg of rice costs £2.10
1kg = 1000g
500g: £1.20 ÷ 500 = £0.0024 per gram
1000g: £2.10 ÷ 1000 = £0.0021 per gram
1000g: £2.10 ÷ 1000 = £0.0021 per gram
2
Question : Which juice offers the best value? 2 litres for £2.80. 1.5 litres for £2.10
£2.80 ÷ 2 = £1.40 per litre
£2.10 ÷ 1.5 = £1.40 per litre
3
Question : Compare 6 pens for £3.60 and 10 pens for £5.50
6 pens: £3.60 ÷ 6 = £0.60 per pen
10 pens: £5.50 ÷ 10 = £0.55 per pen
4
Question : Compare 750ml shampoo for £3.75 and 500ml shampoo for £2.40
750ml: £3.75 ÷ 750 = £0.005 per ml
500ml: £2.40 ÷ 500 = £0.0048 per ml
- Common GCSE Mistakes
- Units: Convert measurements to the same units before comparing.
- Comparison: Do not compare total prices alone; compare cost per unit.
- Calculator: Check division carefully to avoid calculator errors.
- Rounding: Avoid rounding unit costs too early when values are close.
- Exam Tips
- Write down the unit you are comparing, such as per gram or per item.
- Convert quantities to the same units before calculating unit cost.
- Divide price by quantity consistently for every option.
- Keep enough decimal accuracy when two offers are close.
- State clearly which option is the better buy and why.
- If unit costs are equal, say that both offers give the same value.
Skills Used in Best Buys
Ratio
Proportion
Unit Conversions
Percentages
Money Problems
Division
Unit Cost
Calculator Skills
Real-World Problem Solving
Ready to Practise?
Printable Worksheet
Download and print practice questions with answers.
Interactive Quiz
Test your knowledge with instant feedback and hints.
Exam-Style Questions
Timed questions to build confidence for the real exam.
Watch the Best Buys Tutorial
Step-by-step walkthroughs of Best Buys with clear methods and exam tips.
Frequently Asked Questions
It asks you to compare products or offers to determine which gives the best value for money.
Convert to comparable units, calculate cost per unit, then compare the unit costs.
The option with the lower cost per unit.
They provide the same value, as shown in the juice example.
Products may be given in different quantities or units, so converting them allows a fair comparison.
Not by themselves. The source says to compare cost per unit rather than total cost.