Market Maths Strategies

Overview

In this seventh lesson of Year 4 Maths Across Aotearoa, learners use place value to estimate, choose and explain efficient addition and subtraction strategies. They build on previous work with regrouping and number lines by comparing compensation, partitioning and open number-line methods, then apply their thinking to totals from a local market context.

Learning intentions

• WALT estimate answers and decide whether addition or subtraction is needed.
• WALT choose an efficient strategy for numbers to 10,000.
• WALT record our thinking using equations, materials, diagrams or words.
• WALT check an answer using the inverse operation.

Success criteria

• I can solve 2,498 + 376 and explain my strategy.
• I can use compensation, partitioning or an open number line.
• I can estimate before calculating and decide whether my answer is sensible.
• I can check an addition answer with subtraction, or a subtraction answer with addition.

Curriculum links

• Number: use place-value understanding and additive strategies with whole numbers.
• Mathematics and Statistics: communicate mathematical thinking using diagrams, equations and oral explanations.
• Mathematics and Statistics: reason, estimate, check and justify whether a solution is sensible.
• Mathsteasers: deepen understanding through challenging, higher-order problems and multiple possible strategies.

Lesson structure (60 minutes)

1. 0–5 min · Hook and estimate. Display the question “Which is easier: 2,498 + 376 or 2,500 + 376?” using the opening estimation slide and invite learners to estimate silently before sharing with a partner. Students explain what they changed and why an estimate is useful.

2. 5–15 min · Model three strategies. Use place-value materials and the strategy comparison slides to model 2,498 + 376 = 2,874 in three ways: compensation (2,500 + 376 − 2), partitioning (2,000 + 400 + 70 + 8), and an open number line (add 300, then 70, then 6). Students notice which digits change, record one method and help identify the inverse check: 2,874 − 376 = 2,498.

3. 15–22 min · Guided strategy choice. Write 3,602 − 875 and ask learners to estimate first. Model how to partition 875 or use an open number line, then confirm the checkpoint answer 3,602 − 875 = 2,727. Students solve on mini-whiteboards, show a check using the inverse operation, and hold boards up for a quick scan.

4. 22–42 min · Local market totals investigation. Place learners in groups of four with place-value materials, graph paper and the local market totals worksheet. Students solve the Must Do problem first: 2,498 + 376. They then select suitable prices or quantities from the market table to find totals and differences, estimate each answer, and record at least one equation, representation and explanation. One learner builds the numbers, one calculates, one checks, and one prepares the oral or written explanation; rotate roles halfway through.

5. 42–53 min · Share and compare. Use the market investigation and discussion slides to display two or three different solutions. Students explain why their method was efficient, compare exact answers with estimates, and identify any errors caused by place-value confusion. Invite learners who are ready to attempt the Can Do: 5,000 − 1,275 = 3,725, or the Try: show two methods for 4,999 + 126.

6. 53–60 min · Reflect and exit check. Return to the plenary and exit-question slide. Students complete the final question on the worksheet: solve one addition or subtraction calculation, estimate first, and write or draw an inverse check. Finish with a pair-share: “The strategy I would choose next time is … because …”

Resources

• the complete strategy and market maths slide deck
• the local market totals worksheet
• Place-value blocks or bundles of sticks
• Mini-whiteboards, pens and erasers
• Graph paper
• Pencils, rulers and highlighters
• Prepared local market price and quantity table
• Classroom number line or open number-line strips
• Calculators for teacher checking only, if required

Assessment

• Listen for accurate use of place-value language such as thousands, hundreds, tens and ones during modelling and group work.
• Check estimates, strategy choices, recordings and inverse-operation checks on whiteboards and the worksheet; note learners who rely on a written algorithm without explaining why it works.
• Use the exit response to identify whether learners can solve accurately, represent their thinking and judge whether an answer is sensible.

Differentiation

• Support learners with smaller numbers first, concrete place-value materials, a partially marked open number line and sentence starters: “I estimated …”, “I changed … because …”, and “I checked by …”.
• Allow learners to explain orally to a partner or record an annotated diagram instead of writing a full explanation. Pair strategically and pre-teach market vocabulary such as total, difference, cost and change.
• For learners needing further challenge, require two methods for 4,999 + 126, comparison of efficiency, or a newly created market problem with an answer and inverse check.
• For EAL learners and learners with additional needs, use consistent visual symbols for estimate, calculate and check; read problems aloud, reduce copying demands and provide extra processing time.