Jan 15

Maths – Addition and Subtraction

Using the Inverse to Solve Addition and Subtraction (Year 2)

This week in maths, Year 2 have been learning how addition and subtraction are connected by using the inverse. The inverse means doing the opposite operation to help us find a missing number or check an answer. When we know one fact, we can use its inverse to help us solve a related problem.

The children have been working with numbers up to 100 and using cherry diagrams and bar models to represent numbers clearly and spot missing parts.

What do we mean by the inverse?

  • The inverse of addition is subtraction

  • The inverse of subtraction is addition

If we know the total and one part, we can subtract to find the missing part.
If we know the parts, we can add to find the total.

Representing problems with models

Cherry diagrams
These show a whole number with two parts underneath. They are useful for seeing how numbers are made and for finding missing parts.

Bar models
These show the whole as a long bar, split into parts. They help children see the relationship between the total and its parts.

Worked example

Problem:
___ + 7 = 60

We know the total (60) and one part (7). We need to find the missing part.

Step 1: Represent the problem

  • In a cherry diagram, 60 is the whole, with 7 as one part and the missing number as the other part.

  • In a bar model, the full bar is 60. One part is 7, and the remaining part is unknown.

Step 2: Use the inverse
Because the problem is addition, we use subtraction:

60 − 7 = ___

Step 3: Check
___ + 7 = 60

So, the missing number is 53.

3 things to do at home

  1. Missing number sentences
    Write addition or subtraction sentences with a missing number, such as:
    â–¡ + 34 = 80
    72 − □ = 25
    Ask your child to solve them by using the inverse.

  2. Draw it out
    Choose a number up to 100 and split it into two parts. Ask your child to draw a cherry diagram or bar model and then write the matching addition and subtraction facts.

  3. Check the answer
    When your child solves an addition or subtraction, ask them to check it using the inverse. For example, if they add two numbers, can they subtract one to get the other back?

These activities will help build confidence and deepen understanding of how addition and subtraction work together.