**Ratio and proportion** questions are now very common on GCSE exam papers, where they can make up as much as 40% of the paper.

One of the most common ways for examiners to test knowledge of ratio and proportion is using **recipe-style questions**.

Let's look at an example before we try to solve some ourselves.

**e.g. The recipe below shows the ingredients required to make 12 biscuits. **

**a) How much flour is needed to make 9 biscuits instead?**

Firstly, we need to find the Highest Common Factor (HCF) of 12 and 9.

This is **3**.

We now to work out how much flour is needed for 3 biscuits:

12 biscuits = 200 g of flour

**3 biscuits = 50 g of flour** (200 ÷ 4)

As we now know how much flour is needed for 3 biscuits, we can multiply this by three to find the amount needed for 9:

9 biscuits = **150 g of flour **(50 × 3)

So 150 g of flour is needed to make 9 biscuits using this recipe.

**b) How many biscuits can we make if we have 1 kg of flour and plenty of each of the other ingredients?**

In this question, the amount of flour we have is what will limit the amount of biscuits we can make.

We have 1 kg or **1000 g **of flour.

Each batch of 12 biscuits needs 400 g of flour:

1000 ÷ 400 = **2.5 batches of biscuits **

1 batch = 12 biscuits so 2.5 batches = 12 × 2.5 = **30 biscuits**

So 30 biscuits can be made according to this recipe and using 1 kg of flour.

In this activity, we will apply our knowledge of ratio and proportion in recipe-style questions, where we may be asked to find the value of an ingredient required to make an alternative amount or to find how many can be made with a different amount of one ingredient.