GCSE Maths Practice: best-value

Question 4 of 10

Different cereal boxes have different weights and prices. Use unit price to find the best value.

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

Choose one option:

Always compare prices using cost per kilogram.

Understanding Best Value with Weights

Best value problems are a key part of GCSE Maths because they reflect real-life decision making. When items are sold in different weights and prices, it is not possible to compare them fairly just by looking at the total cost. Instead, you must compare how much each option costs for the same amount, usually one kilogram.

In this question, cereal is sold in boxes of different weights measured in grams and kilograms. Because the quantities are different, a direct price comparison would be misleading. Calculating the cost per kilogram removes this problem and allows you to identify the best value option.

The Unit Price Method

The most reliable way to solve best value questions involving weight is to calculate the unit price.

  1. Convert all weights into the same unit, usually kilograms.
  2. Divide the price by the weight in kilograms.
  3. Compare the cost per kilogram for each option.

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

Worked Example

A shop sells flour in three bags:

  • 750 g for £1.95
  • 1 kg for £2.80
  • 2 kg for £5.20

Convert grams to kilograms, then calculate the cost per kilogram:

  • £1.95 ÷ 0.75 = £2.60 per kg
  • £2.80 ÷ 1 = £2.80 per kg
  • £5.20 ÷ 2 = £2.60 per kg

Comparing these values shows which options offer the lowest price per kilogram.

Another Example

Pet food is sold as:

  • 400 g for £1.48
  • 1.2 kg for £4.20
  • 2 kg for £7.40

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

Common Mistakes

  • Forgetting to convert grams: Always convert grams to kilograms before dividing.
  • Comparing prices directly: The cheapest box overall may not be the best value.
  • Dividing the wrong way: Always divide price by weight, not weight by price.

Real-Life Applications

Unit pricing is used widely in supermarkets. Shelf labels often show the price per kilogram or per 100 grams to help shoppers compare products quickly. This skill is also useful when buying ingredients in bulk, comparing special offers, or planning a budget.

Being confident with best value calculations helps you make smarter financial decisions and avoid misleading deals.

Frequently Asked Questions

Why do we use cost per kilogram?
It ensures all options are compared using the same amount.

What if one option is already in kilograms?
You can use it directly without converting.

Is this topic assessed in GCSE exams?
Yes. Best value by weight is common in Foundation papers.

Study Tip

Whenever weights and prices appear together, immediately calculate the unit price before choosing an answer.

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