GCSE Maths Practice: best-value

Question 10 of 10

Spaghetti is sold in different packet sizes. Compare the cost per 100 g carefully.

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\( \begin{array}{l} \text{Which spaghetti packets offer the best value per 100 g?} \end{array} \)

Select all correct options:

Equal unit prices mean more than one answer can be correct.

Higher GCSE Best Value Using Cost per 100 g

At Higher tier GCSE Maths, best value questions often involve products sold in different weights where prices are close together. These questions are designed to test careful calculation and understanding of unit pricing rather than estimation or guesswork.

In this question, spaghetti packets are sold in three different sizes. Although the total prices and weights differ, the correct approach is to compare each option using the same unit, such as cost per 100 g. This makes the comparison fair and manageable.

Why Use Cost per 100 g?

Using cost per 100 g is particularly useful when:

  • Weights are given in grams rather than kilograms
  • Numbers involve decimals
  • You want to avoid converting to kilograms

As long as every option is compared using the same unit, the comparison is valid.

Step-by-Step Method

  1. Check that all weights are measured in grams.
  2. Divide each weight by 100 to find the number of 100 g units.
  3. Divide the price by the number of units.
  4. Compare the unit prices carefully.

The lowest cost per 100 g represents the best value.

Worked Example

A supermarket sells pasta as:

  • 400 g for £0.72
  • 750 g for £1.35
  • 1 kg for £1.80

First, calculate the number of 100 g units:

  • 400 g = 4 units
  • 750 g = 7.5 units
  • 1 kg = 10 units

Now divide price by units:

  • £0.72 ÷ 4 = £0.18 per 100 g
  • £1.35 ÷ 7.5 = £0.18 per 100 g
  • £1.80 ÷ 10 = £0.18 per 100 g

This example shows how different packet sizes can sometimes offer exactly the same value.

Another Higher-Tier Example

Rice is sold as:

  • 500 g for £0.90
  • 1 kg for £1.70
  • 1.5 kg for £2.55

Using cost per 100 g allows a fair comparison without converting to kilograms.

Common Higher-Tier Mistakes

  • Assuming larger packs are always better: Bigger packets are not automatically cheaper per unit.
  • Rounding too early: Small rounding errors can change which options appear equal.
  • Choosing only one answer: Equal unit prices mean multiple answers may be correct.

Real-Life Applications

Supermarkets frequently display cost per 100 g for dry foods such as pasta, rice, cereals, and snacks. This helps customers compare products fairly when packet sizes vary.

Understanding unit pricing ensures you make informed decisions and are not misled by packaging size or price appearance.

Frequently Asked Questions

Can more than one packet be best value?
Yes. If two or more packets have the same unit cost, they offer equal value.

Why not use cost per kilogram?
For smaller weights, cost per 100 g often gives clearer numbers.

Is this common in GCSE Higher exams?
Yes. Equal-value best value questions appear regularly.

Exam Tip

If two unit prices match exactly, trust your calculations — both options are equally good value.

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