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