Year 3 Mathematics · AC9M3A02

Extend and apply knowledge of addition and subtraction facts to 20 to develop efficient mental strategies for computation with larger numbers without a calculator

Known facts such as doubles, complements to 10 and fact families can be extended to tens and hundreds for efficient mental calculation

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Learning goalsSay it simply

Known facts such as doubles, complements to 10 and fact families can be extended to tens and hundreds for efficient mental calculation.

Learning routine: Recall known fact → Adjust place value → Choose strategy → Calculate mentally → Check

Success looks like

  • Extend facts to tens
  • Use bridging
  • Use compensation
  • Use doubles and near doubles
  • Explain mental strategies

Success criteria:

  • Extend facts to tens
  • Use bridging
  • Use compensation
  • Use doubles and near doubles
  • Explain mental strategies
Key conceptTeach from the board

Key idea: Known facts such as doubles, complements to 10 and fact families can be extended to tens and hundreds for efficient mental calculation.

Learning routine: Recall known fact → Adjust place value → Choose strategy → Calculate mentally → Check

mental strategy
a way to calculate without writing every step
compensation
adjust numbers to calculate, then correct the adjustment
friendly number
a nearby number that is easier to use
Clean visual examplesOne-page board

Clean one-page examples

AC9M3A02 - Extend and apply knowledge of addition and subtraction facts to 20 to develop efficient mental strategies for computation with larger numbers without a calculator
Example 1

Known fact Extended fact 7 + 8 = 15 70 + 80 = 150 15 − 8 = 7 150 − 80 = 70

Example 2

198 + 47 → 200 + 47 → 247 − 2 → 245

Example 3

6+9=15 60+90=150 600+900=1500

Example 4

68 + 2 → 70 → 70 + 5 → 75

Curriculum examplesCopied content

The content description and elaborations below show the curriculum ideas taught in this unit. Items marked as teaching context support lesson planning.

  • Content description: extend and apply knowledge of addition and subtraction facts to 20 to develop efficient mental strategies for computation with larger numbers without a calculator
  • E1: partitioning using materials and part-part-whole diagrams to develop subtraction facts related to addition facts, such as 8 + 7 = 15 therefore, 15 \space-\space 7 = 8 and 15\space - \space 8 = 7
  • E2: using partitioning to develop and record facts systematically; for example, “How many ways can 12 monkeys be spread among 2 trees?”, 12 = 12 + 0, 12 = 11 + 1, 12 = 10 + 2, 12 = 9 + 3, …; explaining how they know they have found all possible partitions
  • E3: understanding basic addition and related subtraction facts and using extensions to these facts; for example, 6 + 6 = 12, 16 + 6 = 22, 6 + 7 = 13, 16 + 7 = 23, and 60 + 60 = 120, 600 + 600 = 1200

Australian, Victorian and NSW alignment retained from the previous page

RegionCurriculumClosest mapping
AustraliaAustralian Curriculum v9.0AC9M3A02 — extend and apply knowledge of addition and subtraction facts to 20 to develop efficient mental strategies for computation with larger numbers without a calculator
VictoriaVictorian Curriculum F-10Year 3 Maths: closest match in Algebra. Use this page as a VIC-aligned practice and worksheet reference.
NSWNSW CurriculumStage 2 Maths: closest content focus for Extend and apply knowledge of addition and subtraction facts to 20 to develop efficient mental strategies for computation with larger numbers without a calculator and related outcomes.
Questions and answersWith answers
What is the big idea in this topic?
Known facts such as doubles, complements to 10 and fact families can be extended to tens and hundreds for efficient mental calculation.
What routine should I use?
Recall known fact → Adjust place value → Choose strategy → Calculate mentally → Check
How do I know I am ready to move on?
You can extend facts to tens, use bridging, use compensation, use doubles and near doubles, explain mental strategies and explain how your model or calculation supports the answer.
Practice and reviewReady for practice
  • Counting by ones — Use a known fact or place-value relationship.
  • Compensation not reversed — If you add extra, subtract it later.
  • Strategy chosen by habit — Choose the method that fits the numbers.

  1. Solve 84 − 38 mentally using partitioning or compensation.

  2. A student changes 199 + 26 to 200 + 26 but forgets to adjust. Explain the correction.

Review hint: Follow the routine “Recall known fact → Adjust place value → Choose strategy → Calculate mentally → Check” and use the worked model to check whether your answer is reasonable.

Curriculum alignmentStart here

Known facts such as doubles, complements to 10 and fact families can be extended to tens and hundreds for efficient mental calculation.

Learning routine: Recall known fact → Adjust place value → Choose strategy → Calculate mentally → Check

Success looks like

  • Extend facts to tens
  • Use bridging
  • Use compensation
  • Use doubles and near doubles
  • Explain mental strategies

Success criteria:

  • Extend facts to tens
  • Use bridging
  • Use compensation
  • Use doubles and near doubles
  • Explain mental strategies
Related resourcesKeep teaching

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