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Year 3

Bridge 100 by subtracting in multiples of 10

I can use number facts to 20 to subtract multiples of 10 and bridge 100.

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New
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Year 3

Bridge 100 by subtracting in multiples of 10

I can use number facts to 20 to subtract multiples of 10 and bridge 100.

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Share activities with pupils
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Lesson details

Key learning points

  1. The language of unitising helps us to use number facts to 20 to subtract multiples of 10 crossing the hundreds.
  2. If 14 subtract 6 is equal to 8 then 14 tens subtract 6 tens is equal to 8 tens or 80.
  3. Partitioning the subtrahend helps us to cross the 100s boundary.

Keywords

  • Subtrahend - The number that is to be subtracted. The second number in a subtraction.

  • Minuend - The first number in a subtraction. The number from which another number is to be subtracted.

Common misconception

Lack of fluency with number facts to 20 can hinder progress in applying them to multiples of ten.

Ensure that fluency with number facts to 20 and related subtraction facts is secure or supported so that pupils can apply them.

Rehearse number facts to 20 and the related subtraction facts ahead of this lesson and provide support with these if needed. Make use of base ten manipulatives to help pupils to see the structure especially when bridging through 100.
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.
What is the missing value? 8 tens + tens = 13 tens.
An image in a quiz
Correct Answer: 5, 5 tens, 50
Q2.
What are the addends in this calculation: 90 + 30 + 10 = 130
90, 10 and 130
130, 90 and 10
Correct answer: 90, 30 and 10
30, 10 and 130
Q3.
If I know 6 + 7 = 13, what is 6 tens + 7 tens?
Correct Answer: 13 tens, 130, 13 tens
Q4.
Match the linked equations. Which number facts would you use to solve each equation with multiples of 10?
Correct Answer:3 + 8 = 11,30 + 80 = 110

30 + 80 = 110

Correct Answer:4 + 9 = 13,40 + 90 = 130

40 + 90 = 130

Correct Answer:5 + 7 = 12,50 + 70 = 120

50 + 70 = 120

Correct Answer:6 + 7 = 13,60 + 70 = 130

60 + 70 = 130

Q5.
What is the sum of these addends 40 + 60 + 50 =
Correct Answer: 150, one hundred and fifty
Q6.
What is the missing addend 80 + + 40 = 140?
Correct Answer: 20, twenty

Exit quiz

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6 Questions

Q1.
Which number is the subtrahend in this calculation? 150 - 70 = 80
Correct Answer: 70, seventy
Q2.
Which number is the minuend in this calculation? 130 − 50 = 8 tens
Correct Answer: 130, one hundred and thirty
Q3.
Match the known number fact to its related multiple of ten.
Correct Answer:15 - 9 = 6,150 - 90 = 60

150 - 90 = 60

Correct Answer:14 - 6 = 8,140 - 60 = 80

140 - 60 = 80

Correct Answer:13 - 6 = 7,130 - 60 = 70

130 - 60 = 70

Correct Answer:12 - 5 = 7,120 - 50 = 70

120 - 50 = 70

Correct Answer:16 - 8 = 8,160 - 80 = 80

160 - 80 = 80

Q4.
Calculate 120 - = 80
Correct answer: 40
20
80
Q5.
Which partitioned subtrahend will help you to bridge 100?
Correct Answer:110 - 50,50 = 10 + 40

50 = 10 + 40

Correct Answer:120 - 50,50 = 20 + 30

50 = 20 + 30

Correct Answer:130 - 50,50 = 30 + 20

50 = 30 + 20

Correct Answer:140 - 50,50 = 40 + 10

50 = 40 + 10

Q6.
How would the subtrahend 70 be partitioned in this equation?
An image in a quiz
40 and 30
50 and 20
Correct answer: 60 and 10