This topic summary covers Knowledge Organiser: Best Buy Comparisons within Best Buy for GCSE Mathematics. Revise Best Buy in Ratio & Proportion for GCSE Mathematics with 12 exam-style questions and 22 flashcards. Use this page as part of a wider topic revision path rather than treating it as an isolated fact. It is section 8 of 8 in this topic. Use this topic summary to connect the idea to the wider topic before moving on to questions and flashcards.
Knowledge Organiser: Best Buy Comparisons
Key Terms
- Best buy: The option that gives the most quantity for the lowest price per unit
- Price per unit: Total cost divided by quantity (e.g. pence per gram)
- Multi-buy offer: A deal where buying more reduces the effective cost per item
- BOGOF: Buy One Get One Free — effectively halves the price per item
- Percentage discount: A reduction of a set percentage from the original price
Must-Know Facts
- Always compare using the same unit (price per gram, per litre, per item)
- Lower price per unit = better value, regardless of pack size
- For "3 for 2" deals: you get 3 items but pay for 2
- Apply percentage discounts before comparing unit prices
- Convert units to match before comparing (e.g. kg to g)
- Always show your comparison clearly and state a conclusion
Key Methods
- Method 1: Price per unit = total price ÷ quantity
- Method 2: Quantity per £1 = quantity ÷ total price (higher = better)
- For offers: calculate final effective price first, then find price per unit
- State a clear conclusion: "[Option] is better value because..."
Common Mistakes
- Comparing incompatible quantities: Always compare the same measure — price per gram vs price per gram, not price vs quantity
- Forgetting to apply offers before dividing: With "buy 2 get 1 free", calculate the effective price first (pay for 2, get 3), then find price per unit
- Not stating a conclusion: Always write which option is better value and why — a calculation alone is not a complete answer
- Mixing units: Convert all quantities to the same unit (e.g. all in grams or all in ml) before comparing — 1 kg vs 250 g needs conversion first
Practice questions for Best Buy
Which method correctly compares the value of two products?
Three sizes of shampoo are available: - Travel: 100 ml for 95p - Regular: 300 ml for £2.55 - Family: 500 ml for £4.00 Find the best value size. Show all working.
Quick recall flashcards
What does 'best buy' mean?
The option that gives the lowest cost per unit (per gram, per litre, per item). Calculate by dividing total price by quantity.
What does BOGOF mean?
Buy One Get One Free. You pay for 1 item but get 2 items. Price per item = Normal price ÷ 2.