Maths hiding in cooking: leftovers

Quick answer

When you cook food, you often have leftovers. You can use maths to work out how much is left after serving. This is done by subtracting the amount eaten from the total amount made.

Learning outcome

By the end of this page, you will be able to work out how much food is left after serving by using subtraction and understanding equal groups.

• You can subtract the amount eaten from the total amount made
• You can use pictures or objects to help you solve problems
• You can understand how food is shared into equal groups
• You can solve real-life problems about leftovers

Why this matters

Knowing how to work out leftovers helps you in many situations. When you help cook, you can check if there is enough food for everyone. When you eat at a restaurant or have a party, you can work out if there is enough or if you need more. Understanding how much food is left helps you plan and save money too. In the future, this skill will help you with bigger maths problems like fractions and division.

How it works

When you cook, you make a certain amount of food. After serving, some of it is eaten and some is left. To find out how much is left, you subtract the amount eaten from the total amount made.

1. Count how much food you made in total
2. Count how much was eaten
3. Subtract the amount eaten from the total amount made
4. Find out how much is left

Examples you can see

Imagine you made a pizza that has 12 slices. You and your family eat 7 slices. How many slices are left?

Step 1: You made 12 slices.

Step 2: 7 slices were eaten.

Step 3: 12 - 7 = 5.

Step 4: There are 5 slices left.

Another example: You baked 20 cookies. You gave 8 cookies to your friends. How many cookies are left?

Step 1: You made 20 cookies.

Step 2: 8 cookies were given away.

Step 3: 20 - 8 = 12.

Step 4: There are 12 cookies left.

You can also use objects to help you. For example, use 12 counters or coins to represent slices of pizza. Take away 7 and count how many are left. This helps you see the subtraction clearly.

Try it as a mini adventure

Imagine you are the chef for a picnic in the park. You made 30 sandwiches. You gave 15 sandwiches to your friends and 8 sandwiches to your family. How many sandwiches are left?

Step 1: You made 30 sandwiches.

Step 2: You gave away 15 + 8 = 23 sandwiches.

Step 3: 30 - 23 = 7.

Step 4: There are 7 sandwiches left.

You can act this out with your toys or use small pieces of paper to represent sandwiches. Try to make the problem bigger or smaller to see how the maths changes.

Common mistakes

• Mistake: Forgetting to subtract the amount eaten from the total made.
• Why it happens: Children may think that eating food means adding more food or they might not understand the concept of subtraction.
• Fix: Use objects or drawings to show the total and then take away the amount eaten to see how many are left.
• Mistake: Mixing up the numbers when subtracting.
• Why it happens: When numbers are big or when children are not confident with subtraction, they may swap digits or make errors.
• Fix: Use counting on fingers or a number line to check the answer. Double-check the subtraction.
• Mistake: Not understanding what "left" means.
• Why it happens: Some children may not know that "left" means "remaining" or "what is not used".
• Fix: Use simple language like "what is still there" or "what is not eaten".

Parent and carer guide

Helping your child with cooking maths is easy and fun. Here are some ways you can support them:

• Ask your child to count how many items are in a recipe, then how many are eaten or used.
• Use real food to show subtraction. For example, if you have 10 biscuits and eat 3, ask how many are left.
• Use a number line or counters to help visualise the problem.
• Encourage your child to draw pictures of the problem to help them understand.
• Keep the practice light and fun. Try to make it a game or a story.

Practice questions

1. You made 15 cupcakes. You ate 6. How many are left?
2. You baked 24 muffins. You gave 9 to your sister. How many are left?
3. You cooked 30 pasta dishes. You served 18. How many are left?
4. You made 10 cookies. You gave 4 to your friend. How many are left?
5. You had 25 slices of cake. You ate 12. How many are left?

Answers:

1. 15 - 6 = 9
2. 24 - 9 = 15
3. 30 - 18 = 12
4. 10 - 4 = 6
5. 25 - 12 = 13

FAQ

Why do we need to know about leftovers?

Knowing how much is left helps you plan meals, save food, and make sure there is enough for everyone. It also helps you understand how much food you have used.

Can we use maths to figure out how much food to cook?

Yes! If you know how many people will eat and how much each person will eat, you can work out how much food to make. This helps avoid waste and makes sure everyone gets enough.

How can I help my child practice this at home?

You can make simple problems using food items like fruits, cookies, or pasta. Ask questions like, "If we have 12 apples and eat 5, how many are left?" Use counting, drawing, or objects to make it easier to understand.

What if my child finds subtraction hard?

Use hands-on activities with real objects. For example, use counters or toys to show the problem. You can also use a number line or draw pictures to help them see the subtraction clearly.

Are there any games to practice this?

Yes! You can play a game where you make a pretend recipe and ask your child to work out how much is left after serving. You can also use board games that involve counting and taking away items to practice subtraction.