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Year 5 - Maths

Explain the reasons for changing two-factor multiplication calculations to three-factor calculations

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 reasons for changing two-factor multiplication calculations to three-factor calculations.

Key Notes

  • Times table facts can simplify multiplication calculations using the factors of a number to make the calculation easier.

Vocabulary To Learn

  • array: An array is when items are arranged in rows and/or columns.
  • factor: Factors are whole numbers which exactly divide another whole number.
  • 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.
  • efficient: Working efficiently means finding a way to solve a problem quickly whilst also maintaining accuracy.

Common Mistakes To Avoid

  • Pupils think that the factor that must become the product of two factors is always the largest factor.

3 Quick Questions (With Answers)

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

Times table facts can simplify multiplication calculations using the factors of a number to make the calculation easier. Times table facts can simplify multiplication calculations using the factors of a number to make the calculation easier.

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

An array is when items are arranged in rows and/or columns. Use this word when showing your method, then check your final answer is reasonable.

3. Spot and fix this common maths mistake.

Mistake: Pupils think that the factor that must become the product of two factors is always the largest factor. Correction: Ensure pupils are provided with a range of opportunities to break down factors, identifying where it does make a calculation easier, and also where it doesn't make the calculation easier.

More Lessons In This Unit

Browse all guides in the Year 5 Maths guide library.