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Year 5 - Maths

Explain the use of the commutative and associative laws when multiplying three or more numbers

Multiply 3 or more numbers (commutative and associative laws)

Unit Summary

In this unit pupils will explain the use of the commutative and associative laws to rearrange and simplify calculations when multiplying three or more numbers.

Lesson Summary

You will learn to explain the use of the commutative and associative laws when multiplying three or more numbers.

Key Notes

  • You can change the order of the factors or group them in different ways and the product remains the same.
  • The commutative and associative laws can be used to make calculations more efficient.

Vocabulary To Learn

  • Commutative: The commutative law states that you can write the values of a calculation in a different order without changing the solution; the result is the same. It applies to addition and multiplication.
  • Associative: The associative law states that it doesn't matter how you group or pair values (i.e. which we calculate first), the result is still the same. It applies to addition and multiplication.

Common Mistakes To Avoid

  • Pupils only ever calculate an equation from left to right.

3 Quick Questions (With Answers)

1. Solve this in steps: explain the method from this lesson and why each step matters.

You can change the order of the factors or group them in different ways and the product remains the same. The commutative and associative laws can be used to make calculations more efficient.

2. Use this key word in a maths sentence and explain it clearly. 'Commutative'

The commutative law states that you can write the values of a calculation in a different order without changing the solution; the result is the same. It applies to addition and multiplication. Use this word when showing your method, then check your final answer is reasonable.

3. Spot and fix this common maths mistake.

Mistake: Pupils only ever calculate an equation from left to right. Correction: Ensure pupils are given time to explore where the commutative law might be best used and where the associative law might be better used. Pupils should be expected to reason why they have chosen to adopt a strategy.

More Lessons In This Unit

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