What are missing number problems?

They are sums with a number hidden. A box or a question mark stands for the hidden number.

How do I solve ? + 3 = 7?

Take away. 7 - 3 = 4, so the missing number is 4. Then check: 4 + 3 = 7.

Why are there missing number questions in Year 1?

They help children understand that add and subtract are linked and that the equals sign means the same as.

Can the missing number be 0?

Yes. In 5 + ? = 5 the missing number is 0.

Year 1 missing number problems lesson to download as PDF

This Year 1 missing number problems lesson is written for pupils aged 5-6 and follows the National Curriculum. In short, it shows you how to find the missing number in simple addition and subtraction statements. Before you start, it helps to revise numbers to 100 and place value and addition and subtraction within 20, because this lesson builds on them.

Table of Contents

Year 1 missing number problems lesson: what you will learn

Hello, I am Otto! A missing number problem is like a little puzzle. One number is hiding, and you are the detective who finds it. You already know addition and subtraction, so you have the tools you need.

Starter activity

Put 10 counters in a pot. Hide some under a cup and leave 6 on the table. Ask a friend: "How many counters are under the cup?" Work it out together. Then lift the cup and check. You have just solved 6 + ? = 10!

What is a missing number problem?

Definition: missing number

A missing number is a number we do not know yet. We show it with a box, a question mark or a blank space, like this: 4 + ? = 9. We must find the number that makes the number sentence true.

The whole bar is 9. One part is 4. The other part is missing.

Example 1

Find the missing number: 4 + ? = 9.

Start on 4 and count on to 9: 5, 6, 7, 8, 9. That is 5 steps. The missing number is 5. Check: 4 + 5 = 9.

The equals sign means “the same as”

Definition: equals

The sign = means is the same as. What is on the left must be the same amount as what is on the right. Think of a balance: both sides must weigh the same.

Rule: balance

Both sides of = are worth the same.
The missing number can be on the left or on the right.
10 = 6 + 4 means the same as 6 + 4 = 10.

Example 2

Find the missing number: 12 = ? + 5.

12 is the whole. 5 is one part. The other part is 12 − 5 = 7. So the missing number is 7. Check: 7 + 5 = 12.

Missing numbers in addition

Method: missing number in an addition

Find the total (the biggest number).
Find the part you know.
Take the part away from the total. The answer is the missing part.
Check by adding.

Example 3

Find the missing number: ? + 8 = 15.

The total is 15. One part is 8. 15 − 8 = 7. The missing number is 7. Check: 7 + 8 = 15.

Missing numbers in subtraction

Method: missing number in a subtraction

Look at the sentence 9 − ? = 4. The 9 is the number you start with.
You end with 4. How many did you take away?
Count from 4 up to 9, or work out 9 − 4.
Check by taking away.

Example 4

Find the missing number: 9 − ? = 4.

Start with 9 and end with 4. We took away 9 − 4 = 5. The missing number is 5. Check: 9 − 5 = 4.

Example 5

Find the missing number: ? − 6 = 7.

We start with a number, take away 6 and have 7 left. So we must add 6 back: 7 + 6 = 13. The missing number is 13. Check: 13 − 6 = 7.

Watch out

Do not just put the two numbers you see together. In 9 − ? = 4, the answer is not 13!
Always check by putting your number into the sentence.
The missing number might be the first number, as in ? + 5 = 11.

Using what you know

Key fact: related facts

If 6 + 7 = 13, then 13 − 7 = 6 and 13 − 6 = 7.
Number bonds to 10 help: if 3 + ? = 10, then ? = 7.
Doubles help: ? + ? = 12 means ? = 6.

Example 6

Find the missing number: ? + ? = 14.

Both numbers are the same. This is a double. Half of 14 is 7. So the missing number is 7. Check: 7 + 7 = 14.

Example 7: a story

Ella has some pencils. She gets 5 more and then she has 12. How many did she have at the start?

Write it as a missing number sentence: ? + 5 = 12. 12 − 5 = 7. Ella had 7 pencils at the start.

Did you know?

Detectives and maths solvers use the same trick: work backwards from what you know. A very old kind of puzzle, written in Egypt nearly 4000 years ago, asked "A number and its half make 12. What is the number?"

Otto's tip

Always put your answer back into the number sentence. If both sides match, you have solved the puzzle. A good detective checks the clue!

How to use this Year 1 missing number problems lesson

First, read the key points so that you know where the Year 1 missing number problems lesson is going. Then work through each definition and worked example, and cover the solution before you read it. After that, practise with the missing number problems worksheet and check every question with the worksheet answers. When you feel ready, test yourself with the multiple choice questions or the quick quiz. Finally, sit the missing number problems test and mark it with the test answers.

Also, the starters are a good warm-up, so you can keep the key facts fresh. Moreover, all the pages of this chapter work together, so you can move between them at any time. For example, many pupils read the lesson on Monday, practise on Wednesday and test themselves on Friday. In short, this Year 1 missing number problems lesson gives you everything you need for the chapter.

Missing number problems – Year 1 maths lesson to download as PDF