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Year 3

Use the additive relationship to rearrange and solve equations

I can use the additive relationship to rearrange and solve equations.

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New
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Year 3

Use the additive relationship to rearrange and solve equations

I can use the additive relationship to rearrange and solve equations.

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Share activities with pupils
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Lesson details

Key learning points

  1. When a whole is missing, add the parts together.
  2. To find a missing part, subtract the other part from the whole.
  3. Rearrange the equation to make it easier to calculate the missing number.

Keywords

  • Equation - An equation shows that one number or calculation is equal to another.

  • Rearrange - Rearrange means to change an equation. It could mean moving the parts or the whole or changing it from an addition into a subtraction equation.

Common misconception

Pupils may use the wrong operation to find missing numbers, adding when they should be subtracting or vice versa.

Encourage pupils to draw bar models, focusing on the whole in the problem. They should also write problems, understanding where the missing number is and rearranging equations so that they can calculate the answers.

The numbers used in this lesson should be very familiar to the pupils and they are expected to calculate using mental and informal methods. Base ten blocks may be helpful as will number lines and bar models to represent the problems. Task A would make a good collaborative task for pupils.
Teacher tip

Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

Lesson video

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Starter quiz

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6 Questions

Q1.
Which number in this equation is the sum? 18 + 8 = 26
8
18
Correct answer: 26
Q2.
Which number is this equation is the minuend? 43 − 10 = 33
Correct answer: 43
33
10
Q3.
Calculate the missing number in this equation: − 14 = 10
Correct Answer: 24, twenty-four
Q4.
Calculate the missing number in this equation: 35 − = 25
Correct Answer: 10, ten
Q5.
What is the difference between 40 and 140?
Correct Answer: 100
Q6.
Calculate the missing number in this equation: = 71 − 11
Correct Answer: 60, sixty

Exit quiz

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6 Questions

Q1.
Which of these are equations?
Correct answer: 24 + 10 = 34
Correct answer: 96 − 20 = 76
5 + 5 + 10
Correct answer: 10 + 5 = 5 + 10
Q2.
The equation 16 + 20 = 36 has been rearranged in different ways. Match up the parts of the equations to make them correct.
Correct Answer:20 = ,36 − 16

36 − 16

Correct Answer:36 = ,20 + 16

20 + 16

Correct Answer:16 = ,36 − 20

36 − 20

Q3.
Find the missing part. 20 + $$\square$$ = 110
70
80
Correct answer: 90
100
Q4.
What is the missing number? 65 = $$\square$$ − 30
Correct Answer: 95, ninety-five
Q5.
There are some cherries in a bowl. Polly eats 12 cherries. There are 21 left. How many cherries were in the bowl to start with?
9
23
Correct answer: 33
Q6.
There are 45 cherries in a bowl. Petra eats some cherries. There are 15 left. How many cherries did Petra eat?
Correct Answer: 30, thirty

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