Compare value for money with unit prices, scale recipes up and down, find the most a recipe can make, and change money between currencies.
What you will learn
- Use the unitary method to scale a cost
- Decide which pack is the better buy
- Scale a recipe and find which ingredient runs out first
- Change pounds to another currency and back
Compare the same amount
The unitary method means finding the value of one first, then multiplying.
If 6 pens cost £4.80, one pen costs £4.80 ÷ 6 = 80p, so 10 pens cost 10 × 80p = £8.00.
To find the better buy, work out what the same amount costs in each pack: 100 g, 1 litre or one item.
- Pack A: 400 g for £2.60, Pack B: 750 g for £4.50
- Pack A: £2.60 ÷ 4 = 65p per 100 g
- Pack B: £4.50 ÷ 7.5 = 60p per 100 g
- Pack B is the better value
For multi-packs holding different numbers of items, compare the price of one item: 4 for £3.00 is 75p each, and 6 for £4.20 is 70p each, so the pack of 6 is cheaper by 5p each.
The bigger pack is often, but not always, better value. Check every time.
The rest of this lesson and its 8 practice questions are locked.
In this lesson
- Compare the same amount
- Recipes
- Exchange rates
- Try it: One first
8 practice questions, marked as you go; about 25 minutes in all.
Key terms
Unitary method, Same amount, Every
In this unit: Ratio and proportion
Convert units and use scales, write and simplify ratios, share amounts in a ratio, compare best buys and exchange rates, and solve direct and inverse proportion problems.
- Units, conversions and scales
- Writing and simplifying ratios
- Sharing and using ratios
- Best buys, recipes and exchange rates
- Direct and inverse proportion