GCSE Maths Practice: best-value

Question 6 of 10

Different pack sizes are shown. Use unit price to decide which option gives the best value.

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\( \begin{array}{l} \text{Which pack gives the best value for money?} \end{array} \)

Choose one option:

Always compare prices using cost per kilogram.

Best Value Problems Using Weight

Best value questions are designed to test your ability to compare prices fairly when items come in different sizes. In everyday shopping, products are often sold in a range of weights and prices, which can make comparisons confusing. GCSE Maths uses these problems to help you practise making sensible financial decisions.

When weights are different, the only fair way to compare prices is by calculating the cost for the same amount, usually one kilogram. This method removes the effect of different pack sizes and allows you to see which option is genuinely cheaper.

Using Unit Price to Compare Value

The key skill in best value questions is finding the unit price. For products sold by weight, this is usually the cost per kilogram.

  1. Check all weights and convert grams to kilograms if needed.
  2. Divide the price by the weight in kilograms.
  3. Compare the unit prices.

The lowest unit price represents the best value for money.

Worked Example

A shop sells sugar in three different bags:

  • 400 g for £0.92
  • 1 kg for £2.40
  • 2 kg for £4.50

Convert grams to kilograms, then calculate cost per kilogram:

  • £0.92 ÷ 0.4 = £2.30 per kg
  • £2.40 ÷ 1 = £2.40 per kg
  • £4.50 ÷ 2 = £2.25 per kg

Comparing these values shows which bag offers the lowest cost per kilogram.

Another Example

Chocolate is sold as:

  • 200 g for £0.78
  • 500 g for £1.95
  • 1 kg for £4.10

After converting all weights to kilograms, divide the price by the weight to compare fairly.

Common Mistakes to Avoid

  • Not converting units: Always convert grams to kilograms before calculating.
  • Choosing the cheapest pack: The lowest total price is not always the best value.
  • Incorrect division: Divide price by weight, not weight by price.

Real-Life Applications

Supermarkets often display unit prices on shelf labels to help customers compare products quickly. This same skill is useful when buying food, pet supplies, or household goods in bulk. Understanding best value helps you manage money wisely and avoid misleading offers.

Frequently Asked Questions

Why do we compare cost per kilogram?
It allows all options to be compared using the same amount.

What if one option is already 1 kg?
You can use its price directly as the cost per kilogram.

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

Study Tip

Whenever weights and prices are given together, calculate the unit price before making a decision.

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