Missing number equations

Quick answer

You can find the missing number in an equation by using the opposite operation. If you see 5 + ? = 9, you can think: "What number added to 5 makes 9?" The answer is 4, because 5 + 4 = 9. You can also subtract: 9 – 5 = 4.

Learning outcome

By the end of this page, you will be able to find the missing number in simple equations using addition, subtraction, multiplication, or division.

• You can solve equations like 5 + ? = 12 or ? × 3 = 15.
• You understand that the equals sign means "the same as" and both sides must balance.
• You can use subtraction to check your answer in addition problems and division to check multiplication.
• You can explain how you found the missing number in a simple equation.

Why this matters

Missing number equations are the first step towards algebra. They help you think like a mathematician and solve puzzles. You use these skills when you share cookies fairly, figure out how many toys you need to buy, or plan how long a trip will take. These problems help you get ready for more advanced maths like solving for x in later years.

How it works

Missing number equations are like puzzles. You have a number sentence with a box or a question mark, and you must figure out what number belongs there.

1. Look at the whole equation.
2. Decide what operation (addition, subtraction, multiplication, or division) is used.
3. Think: "What number will make the equation true?"
4. Try your number and check it by solving the equation.

For example, in 7 + ? = 15, you think: "What number added to 7 makes 15?" You can subtract: 15 – 7 = 8. So, 7 + 8 = 15. The missing number is 8.

Examples you can see

Here are some simple missing number equations with examples you can imagine or draw:

Try drawing these on paper or using blocks to help you solve them. For example, if you have 4 groups of 5 blocks, you have 20 blocks in total. So 4 × 5 = 20. If you know 4 × 5 = 20, then 20 ÷ 4 = 5.

Try it as a mini adventure

Adventure: The Magic Number Cave

You are a brave explorer who finds a magical cave with puzzles. Each puzzle has a box that needs a number to open the next door. You must solve the equations to find the right number.

1. First puzzle: 6 + ? = 13
2. Second puzzle: ? × 2 = 10
3. Third puzzle: 15 – ? = 9
4. Fourth puzzle: ? ÷ 3 = 7

Can you find the magic numbers to open all the doors? Use what you know about operations to solve each one!

Common mistakes

• Mistake: Thinking that the box always means to add.
  Why it happens: Confusing the symbol for a missing number with a plus sign.
  Fix: Remember that the box can be any operation. Look at the whole equation.
• Mistake: Adding when you should subtract.
  Why it happens: Not reading the equation carefully.
  Fix: Ask yourself: "What operation do I need to undo this?"
• Mistake: Using the wrong number in a multiplication or division equation.
  Why it happens: Guessing without checking.
  Fix: Multiply or divide your answer to see if it matches the other side.

Parent and carer guide

Helping your child with missing number equations is simple and fun:

1. Ask your child to explain their thinking. For example, "How did you find the missing number?"
2. Use real-life examples like sharing snacks or counting toys.
3. Let them draw pictures or use objects to solve problems.
4. Don’t rush. Encourage them to try different numbers if the first guess doesn’t work.
5. Check their answer by solving the equation again with their number.

Remember: It’s okay to make mistakes. They help you learn!

Practice questions

1. 5 + ? = 12
   Answer: 7
2. ? – 4 = 9
   Answer: 13
3. 3 × ? = 18
   Answer: 6
4. ? ÷ 5 = 4
   Answer: 20
5. 7 + ? = 14
   Answer: 7
6. ? × 6 = 30
   Answer: 5
7. 12 – ? = 5
   Answer: 7
8. ? ÷ 3 = 9
   Answer: 27
9. 8 + ? = 15
   Answer: 7
10. ? × 4 = 24
    Answer: 6

FAQ

What is a missing number equation?

A missing number equation is a maths sentence where one number is missing and you must find it. It looks like 5 + ? = 10 or ? × 3 = 12.

How do I know which operation to use?

Look at the symbol in the equation. If there is a plus sign (+), you might need to subtract to find the missing number. If there is a multiplication sign (×), you might need to divide.

Can I use a calculator?

Yes, but try to solve the equation first without a calculator. This helps you understand the math better.

Why do I need to learn this?

Missing number equations help you think logically and prepare for algebra. You use these skills in everyday life, like when you’re sharing cookies or planning a trip.

How can I practice at home?

Try making up your own equations with numbers you like. You can use toys, food, or drawings to make the problems real and fun.