Number • Difference · Stretch and explain

Make a true claim

Choose two different two-digit numbers and find the difference. Make another pair with the same difference but a different sum. Explain what changed and what stayed the same.

Give it a go

Try ideas with the activity tools, draw your thinking, or explain it in words. There may be more than one useful response. This activity does not save or submit your work.

What this explores

Difference and additive invariance. Use the positive distance between the two numbers as the difference. Adding the same amount to each number preserves this distance but changes their sum.

A starting nudge

What happens to the difference when you add the same amount to both numbers? What happens to the sum?

Take it further

Can you make a third pair with the same difference and a smaller sum?

For teachers

Ask students to compare strategies and explain what makes their response valid. These difficulty bands are provisional, not verified curriculum or year-level alignments.

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