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.

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

Students should be comfortable with addition and subtraction facts to 20, simple equal groups and number sentences, and using symbols to represent an unknown or repeated relationship. Revisit a concrete or pictorial model first if the symbols are not yet meaningful.

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

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.

• 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. If 7 + 8 = 15, what is 70 + 80?

   • 150
   • 15
   • 1 500
   • 78

2. Complete the bridge.

   Prompt: 68 + 7 = 68 + 2 + □ = 75

3. What is 198 + 47 using compensation?

   • 245
   • 255
   • 235
   • 145

4. Solve 49 + 50 mentally and explain the strategy.

5. Match the calculation to a useful strategy.

   Match: 68 + 7 • 49 + 50 • 198 + 34 ↔ compensation • near doubles • bridge to next ten

6. Complete the extended fact.

   Prompt: 15 − 8 = 7, so 150 − 80 = □.

1. Find three different mental strategies for 297 + 58 and compare them.

2. Create a chain of four calculations that all use the known fact 9 + 6 = 15 at different place values.

Explain the reasoning, not only the final answer.

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.

• I can extend facts to tens.
• I can use bridging.
• I can use compensation.
• I can use doubles and near doubles.
• I can explain mental strategies.

Quick check: Use 7 + 8 to solve 70 + 80. • Solve 68 + 7 mentally. • Solve 198 + 47.

Read the topic guide and use the teacher slide for instruction. Students can then use the worksheet for written work, open Practice for supported feedback, or take the Test when they are ready.

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

• Australian Curriculum Version 9.0 — ACARA
• Victorian Curriculum — VCAA
• NSW Curriculum — NESA

Official curriculum sites are the source of record.

• AC9M3A01 — Addition and Subtraction as Inverse Operations
• AC9M3A03 — Multiplication Facts for 3, 4, 5 and 10
• All Year 3 Mathematics topics

Curriculum equivalents for Extend and apply knowledge of addition and subtraction facts to...

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

These references identify matching or closely related learning. Curriculum sequence, terminology and depth vary, so teachers should use the mapped skill and lesson difficulty to confirm suitability.

Australian Curriculum v9.0 is the canonical source for this SkillrHub lesson. Victoria and NSW entries name the closest published state codes or outcomes; international entries are planning references rather than claims of identical curricula.