GCSE Maths Practice: best-value

Question 1 of 10

Cleaning spray bottles come in different sizes and prices. Use unit price to find the best value.

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\( \begin{array}{l} \text{Cleaning spray bottles:} \\ \text{A: 600 ml for £2.10} \\ \text{B: 750 ml for £2.50} \\ \text{C: 1 L for £3.60} \\ \text{Which option offers the best value?} \end{array} \)

Choose one option:

Keep calculations exact until the final comparison.

Higher GCSE Best Value with Decimals and Mixed Units

At Higher tier, best value questions become more challenging by using awkward numbers, decimals, and mixed units such as millilitres and litres. The aim is not only to test whether you know the method, but whether you can apply it accurately and carefully under exam conditions.

In this question, cleaning spray bottles are sold in different volumes measured in millilitres and litres, with prices that do not divide neatly. A quick guess based on price or size alone is very likely to be wrong. The only reliable method is to calculate the unit price.

The Core Method: Cost per Litre

For liquids, the unit price is usually the cost per litre. At Higher tier, accuracy is essential.

  1. Convert all volumes into litres (for example, 600 ml = 0.6 L).
  2. Divide the total price by the volume in litres.
  3. Compare the unit prices carefully, paying attention to decimal places.

The option with the lowest cost per litre gives the best value.

Worked Example

A supermarket sells disinfectant spray as:

  • 500 ml for £1.85
  • 750 ml for £2.55
  • 1.2 L for £3.90

Convert volumes to litres and calculate cost per litre:

  • £1.85 ÷ 0.5 = £3.70 per litre
  • £2.55 ÷ 0.75 = £3.40 per litre
  • £3.90 ÷ 1.2 = £3.25 per litre

Comparing these values shows which option offers the lowest unit cost.

Another Higher-Tier Example

Window cleaner is sold as:

  • 400 ml for £1.36
  • 900 ml for £2.97
  • 1.5 L for £5.10

Convert all volumes to litres and divide price by volume. Careful decimal handling is required to avoid small but costly errors.

Common Higher-Tier Mistakes

  • Forgetting unit conversion: Failing to convert millilitres to litres will give incorrect results.
  • Rounding too early: Rounding during calculations can change which option appears cheapest.
  • Comparing prices directly: Larger bottles often cost more overall but may still be better value.

Real-Life Applications

Higher-level unit pricing is used when comparing household cleaning products, fuel prices, paint, and bulk liquids. Supermarkets often rely on customers not checking unit prices carefully, especially when numbers are awkward.

Being confident with these calculations helps you make informed purchasing decisions and avoid misleading deals.

Frequently Asked Questions

Should I always convert to litres?
Yes. Using a single unit ensures a fair comparison.

How accurate do my decimals need to be?
At Higher tier, keep at least two decimal places until the final comparison.

Is this common in GCSE Higher exams?
Yes. Best value questions with decimals and mixed units appear regularly.

Exam Tip

Never guess based on size or price. Always calculate the unit cost carefully, and double-check your conversions.

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