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Year 3

Identify knowns and unknowns in addition equations

I can identify knowns and unknowns in addition equations.

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Year 3

Identify knowns and unknowns in addition equations

I can identify knowns and unknowns in addition equations.

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Share activities with pupils
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Lesson details

Key learning points

  1. If the sum is missing, you add the addends.
  2. If an addend is missing, subtract the other addend from the sum to calculate the missing value.
  3. When the numbers are close together, add on to find the difference.

Keywords

  • Addend - An addend is a number added to another.

  • Sum - The sum is the the total when numbers are added together.

  • Difference - The difference is the result after subtracting one number from another.

Common misconception

Pupils may confuse the parts and the whole in an equation, especially when there is a missing number.

Bar models are helpful for representing and understanding the parts and the whole. Ensure that pupils understand that minuend and sum both represent a whole. Allow lots of opportunities for pupils to sketch bar models.

Base ten blocks may be helpful for pupils when subtracting. Number lines representations may also be helpful, especially for comparing the relative size of numbers and understanding whether they are close together or far apart.
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Licence

This content is © Oak National Academy Limited (2025), 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? 100 = 20 + 80
Correct answer: 100
80
20
Q2.
Which of these are parts in an equation?
sum
Correct answer: addend
Correct answer: difference
minuend
Q3.
What is the missing sum in this bar model?
An image in a quiz
Correct Answer: 180, one hundred and eighty
Q4.
What is the value of the missing part in this bar model?
An image in a quiz
Correct Answer: 120, one hundred and twenty
Q5.
What could the missing addends in this bar model be?
An image in a quiz
Correct answer: 70 and 70
80 and 40
Correct answer: 90 and 50
110 and 40
Q6.
Which equations could be represented by the bar model?
An image in a quiz
260 + 40 = 300
Correct answer: 260 − 110 = 150
Correct answer: 130 + 130 = 260
260 = 360 − 100

Exit quiz

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6 Questions

Q1.
Which number represents the difference in this equation? 25 − 15 = 10
25
15
Correct answer: 10
Q2.
Match the keywords to their meanings.
Correct Answer:addend,A number added to another.
tick

A number added to another.

Correct Answer:difference,The result after subtracting one number from another.
tick

The result after subtracting one number from another.

Correct Answer:sum,The total when numbers are added together.
tick

The total when numbers are added together.

Q3.
What is the missing part in this bar model?
An image in a quiz
Correct Answer: 13, thirteen
Q4.
What is the value of the missing part in this bar model?
An image in a quiz
Correct Answer: 5, five
Q5.
Which pairs of numbers have a difference of 3?
Correct answer: 17 and 20
22 and 24
Correct answer: 27 and 24
28 and 30
Q6.
How could you calculate the missing part in this bar model?
An image in a quiz
415 + 230 =
Correct answer: 415 − 230 =
Correct answer: 230 + ___ = 415
230 − 415 =

Additional material

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