lesson
Rearrange to make useful groups
1 · Learn
A factor pair multiplies to make a number. For 24, pairs include 1 and 24, 2 and 12, 3 and 8, and 4 and 6.
You can regroup multiplication without changing its product. For 4 × 7 × 5, combine 4 × 5 first to make 20, then multiply by 7. Multiplying by 1 leaves an amount unchanged; multiplying by 0 gives 0.
Dividing by one leaves the amount unchanged too. Sharing 24 counters into just one group puts all 24 in that group: 24 divided by 1 is 24. Do not confuse this with dividing by zero.
2 · Worked example
I work out 6 × 5 × 2 as 6 × 10 = 60. This does not mean I can rearrange subtraction or division in the same way.
3 · Your turn
Find 8 × 3 × 5, 42 × 1 and 42 × 0. Give two factor pairs of 18.
Check your answer
120; 42; 0. Factor pairs include 1 and 18, 2 and 9, 3 and 6.
4 · Apply your learning
Build rectangle arrays for a small number and list its factor pairs without counting reversed pairs as new pairs.
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