Year 2 Mathematics · AC9M2N04

Addition and subtraction strategies

Add and subtract one- and two-digit numbers using part-part-whole reasoning, number sentences, mental strategies, number lines, hundreds charts and informal written…

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Learning goalsSay it simply

Students solve addition and subtraction problems by choosing strategies that make the numbers easier to work with. They connect concrete materials, bar models, number lines, hundreds charts and number sentences so the calculation always stays linked to the problem situation.

  • Use part-part-whole reasoning to identify a whole and its parts.
  • Represent a problem with a bar model and a number sentence.
  • Use doubles, near doubles, bridging to 10 and bridging through tens.
  • Partition two-digit numbers into tens and ones to calculate mentally.
  • Use number lines, hundreds charts and informal jottings to keep track of steps.
  • Recognise that adding zero leaves a number unchanged.
  • Use the inverse relationship between addition and subtraction to check reasoning.
Clean visual examplesOne-page board

Clean one-page examples

AC9M2N04 - Addition and subtraction strategies
Example 1

Support: use counters, ten frames, base-ten blocks, open number lines and completed bar-model templates.

Example 2

Core: ask students to solve the same calculation with two strategies and choose the more efficient method.

Example 3

Extension: give missing-number equations such as 38 + □ = 65 or □ − 27 = 41 and ask students to justify their strategy.

Example 4

: use associative thinking, partitioning, rearranging, regrouping, near doubles and bridging to 10.

Curriculum examplesCurriculum examples

Content description: add and subtract one- and two-digit numbers, representing problems using number sentences, and solve using part-part-whole reasoning and a variety of calculation strategies.

  • E1: use associative thinking, partitioning, rearranging, regrouping, near doubles and bridging to 10.
  • E2: use doubles, near doubles, part-part-whole knowledge, bridging tens and partitioning for two-digit calculations.
  • E3: represent addition and subtraction problems with bar models and matching number sentences.
  • E4: use mental strategies and informal written jottings, including recognising that adding zero leaves the number unchanged.
  • E5: use physical or mental number lines and hundreds charts, moving in tens and ones.
  • E6: use First Nations Australians’ stories and dances as a teaching context for balance and the connection between addition and subtraction.
Questions and answersWith answers

Key idea: Addition can join parts or find a total. Subtraction can take away or find a missing part. Strategies help students work efficiently and explain their thinking.

Remember

  • Represent with number sentences
  • Use part–part–whole
  • Add two-digit numbers
  • Subtract two-digit numbers
  • Explain strategies

Quick questions

  • Solve 47 + 25 using partitioning.
  • Write a number sentence for 63 minus 28.
  • Use an inverse fact to check 82 − 35.
  • Explain your strategy for 58 + 19.

If an answer is uncertain, return to the model and explain what each part represents before calculating or drawing a conclusion.

Practice and reviewReady for practice
  • Counting by ones when a larger jump is available: prompt students to look for tens, doubles or a friendly benchmark.
  • Changing the value while partitioning: every split must recombine to the original number.
  • Writing a number sentence that does not match the story: identify the whole and parts first.
  • Forgetting the second part of a bridge: after reaching 10 or the next ten, the leftover amount still has to be added or subtracted.
  • Ignoring place value: 4 ones + 8 ones makes 12 ones, which is 1 ten and 2 ones.
  • Treating subtraction as only take-away: subtraction can also compare quantities or find a missing part/difference.

Model one strategy at a time, then deliberately mix problem types so students must choose a suitable method rather than repeat the previous example. Use the Teacher Slides for explicit instruction, then move to the worksheet, Practice or Test depending on readiness.

Curriculum alignmentStart here

Students solve addition and subtraction problems by choosing strategies that make the numbers easier to work with. They connect concrete materials, bar models, number lines, hundreds charts and number sentences so the calculation always stays linked to the problem situation.

  • Use part-part-whole reasoning to identify a whole and its parts.
  • Represent a problem with a bar model and a number sentence.
  • Use doubles, near doubles, bridging to 10 and bridging through tens.
  • Partition two-digit numbers into tens and ones to calculate mentally.
  • Use number lines, hundreds charts and informal jottings to keep track of steps.
  • Recognise that adding zero leaves a number unchanged.
  • Use the inverse relationship between addition and subtraction to check reasoning.
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