Year 2

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We can work out the missing number in a number sentence

Year 2 Unit 17

What we are learning:

  • ‘Missing number’ problems are tricky but all the work we have done around place value and related facts will really help with these.
  • It is important to talk about these and ask questions before presenting them in writing as missing number questions. So once your child knows the addition and subtraction facts for 10 and the different ways of making 10 (we call these the ‘number bonds)’ you can ask them questions like, What do we add to 7 to make 10? You can vary this by asking, I am going to say and number and I want you to tell me what number goes with it to make 10.
    Also try this with the number bonds for 20.
    Then record what this could look like when written down: 7 + ? = 10 so that your child can see what a missing number problem looks like.
  • The missing number can be in different places in number sentences and the questions that children find the most difficult are where the missing number is at the start of the number sentence.
    The different ways of writing these are: 7 + 10 = ? 7 + ? = 17 ? + 10 = 17
  • When you do start looking at written missing number problems make sure that you read (interpret) the sentence out loud in different ways.
  • For example for 14 + ? = 35 we could read this in the following ways to begin to understand the question: 14 and some more make a total of 35.
    Add something to 14 so I have a total of 35. I have fourteen and I count on some more to give a total of 35. Because your child now knows that subtraction is the inverse of addition they could re – write this number
    sentence as 35 – 14 = ? and then check that this is correct.

Activities you can do at home:

Activity 1 Practical ways to find the missing number
Using the Abacus Board for 14 + ? = 35. Read the question together in different ways as outlined above. Draw the correct number of circles in the tens and units (one ten and four units). Ask, How many more do you need to draw to have a total of 35? How many tens and how many units?
You can draw these in a different colour.

Alternatively draw a place value chart like this. Place one counter (or draw circles) in the tens column and four counters in the units column and ask, How many more do you need to draw to have a total of 35? How many tens and how many units?

Use the abacus board or the place value chart and try the same for subtraction. 36 – ? = 24. Put three counters in the tens column and 6 counters in the units column – cover up/ remove the counters until you have 24 left. Ask, How many did you take away? Try with other questions: 35 – ? = 12. And with questions that cross the tens boundary 52 – ? = 34. Your child needs to do some exchanging here.

Good questions to ask:

What number is missing from this sentence?
How can you work it out?
What do you have to do to work it out?

If your child:

Finds it difficult to identify missing numbers
Use more practice on addition and subtraction number bonds first. Finding missing numbers is more difficult than it might look!

Extension Activity

Please use this activity when you think your child understands the unit of work. It will deepen and extend your child’s understanding of this unit.


Extension activity (PDF)