GCSE Maths Practice: best-value

Question 2 of 10

Different bottle sizes and prices are shown. Compare them carefully to find the best value.

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\( \begin{array}{l} \text{Three options for bottled water:} \\ \text{A: 500 ml for £0.50} \\ \text{B: 1 L for £1.00} \\ \text{C: 2 L for £1.60} \\ \text{Which option gives the best value?} \end{array} \)

Choose one option:

Always compare prices using the same unit, such as cost per litre.

What Does “Best Value” Mean?

Best value problems appear frequently in GCSE Maths and test your ability to compare prices fairly when quantities are different. The key idea is that prices alone cannot be compared unless the amounts are the same. A larger item may cost more overall but still be better value if it costs less per unit.

In this question, bottled water is sold in different volumes for different prices. To make a fair comparison, each option must be converted to the same unit price, such as cost per litre. This allows you to see which option gives you more for your money.

The Method: Cost Per Unit

The standard method for best value questions is to calculate the cost per unit. This means dividing the total price by the amount you receive.

  1. Identify the unit you are comparing (litres).
  2. Convert all quantities into the same unit if needed.
  3. Divide the price by the number of litres.
  4. Compare the results.

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

Worked Example

A shop sells juice in three different bottles:

  • 750 ml for £0.90
  • 1.5 L for £1.50
  • 2 L for £2.20

First, convert all volumes to litres if necessary. Then calculate the cost per litre:

  • £0.90 ÷ 0.75 = £1.20 per litre
  • £1.50 ÷ 1.5 = £1.00 per litre
  • £2.20 ÷ 2 = £1.10 per litre

Comparing these values shows which bottle offers the lowest price per litre.

Another Example

Toilet paper is sold as:

  • 4 rolls for £2.40
  • 6 rolls for £3.30
  • 9 rolls for £5.40

Divide the price by the number of rolls to find the cost per roll, then compare.

Common Mistakes

  • Comparing total prices only: The cheapest item overall is not always the best value.
  • Not converting units: Always convert millilitres to litres when needed.
  • Incorrect division: Divide price by quantity, not quantity by price.

Real-Life Uses

This skill is used every day when shopping. Supermarkets often show price-per-unit labels to help customers compare products quickly. Fuel prices are compared by cost per litre, and phone contracts are compared by cost per gigabyte.

Understanding best value helps you avoid misleading deals and manage money more effectively.

Frequently Asked Questions

Do I always use cost per unit?
Yes. Whenever quantities are different, converting to a unit price allows a fair comparison.

What if units are different?
Convert them first so all options use the same unit.

Is this topic assessed in GCSE exams?
Yes. Best value questions are common on Foundation papers.

Study Tip

If you see prices and quantities together, always pause and calculate the unit cost before choosing an answer.

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