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Year 6

Use mental strategies and known facts to calculate the value of a missing part

I can use mental strategies and known facts to calculate the value of a missing part.

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New
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Year 6

Use mental strategies and known facts to calculate the value of a missing part

I can use mental strategies and known facts to calculate the value of a missing part.

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Lesson details

Key learning points

  1. Drawing a model for a simpler problem helps us to solve more complicated problems.
  2. Known facts can be used to calculate the value of a missing part.
  3. Mental strategies can be used to calculate the value of a missing part.

Keywords

  • Represent - To represent something means to show something in a different way

  • Addend - Addends are any numbers added together.

Common misconception

Pupils struggle to represent the problem as a repeated subtraction equation.

Simplify problems by using numbers within 10 at first to reveal the structure of the problem. By doing this, you can show how both the subtraction and addition equations relate, which can help you to find the value of the missing parts or whole.

Encourage pupils to consider the efficiency of their calculations when deciding whether to use repeated subtraction or to add the known parts first. It is often more helpful to add the known parts first where there are lots of parts, leaving just one subtraction to take place.
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.
Calculate the missing addend in this bar model.
An image in a quiz
Correct Answer: 680
Q2.
What is the unknown in this problem? Jacob makes a cake using flour, butter and sugar. He uses 500g of flour and 200 g each of butter and sugar.
Correct answer: The mass of the cake batter.
The mass of the flour.
The mass of the butter.
The mass of the sugar.
Q3.
Which equation represents this image?
An image in a quiz
Correct answer: w + y + ___ = bl
w + bl + y = ___
bl + ___ + w = y
Q4.
Which two addends would make the total of 375?
420
Correct answer: 260
Correct answer: 115
135
Q5.
Calculate using an efficient strategy. Aisha buys two books. One costs £12.99 and one costs £7.99 What is the total cost of the books? £
Correct Answer: 20.98, £20.98
Q6.
Complete the column subtraction to find the difference.
An image in a quiz
Correct Answer: 34.56

Exit quiz

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6 Questions

Q1.
True or false. The missing part can only be found by using a repeated subtraction equation.
An image in a quiz
True
Correct answer: False
Q2.
Which equations represent this bar model?
An image in a quiz
Correct answer: 36 − 16 − 8 = ?
36 - 8 + 16 = ?
Correct answer: 16 + 8 + ? = 36
16 − 8 + ? = 36
Q3.
Which equations could solve this problem? Jun is making a fruit drink. He has 1.5 l altogether. He has 0.8 l of orange juice and 300 ml of pineapple juice. The rest is water. How much water is needed?
1.5 l − 0.8l − ___ = 300 ml
Correct answer: 1.5 l − 0.8 l − 300 ml = ___
300 ml + 0.8 l + 1.5 l = ___
Correct answer: 300 ml + 0.8 l + ___ = 1.5 l
Q4.
Solve this missing number problem by adding the known parts first. The missing part is .
An image in a quiz
Correct Answer: 30
Q5.
Use repeated subtraction. Aisha walks for 90 minutes from home to the local pool. She walks for 35 minutes, rests for 10 minutes then continues. For how much longer does she walk? minutes.
Correct Answer: 45
Q6.
Alex is making a fruit drink. He needs 1.5 l altogether. He pours 0.8 l of orange juice and 300 ml of pineapple juice. The rest of the drink is water. How much water is needed? l
Correct Answer: 0.4 , 0.4 l, 400 ml