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Year 5 - Maths

Explain how to use the factor pairs of 100 to solve calculations efficiently

Use common factors and multiples to solve calculations efficiently

Unit Summary

In this unit pupils will explain how to identify common factors and multiples and use this knowledge of properties of number along with knowledge of the commutative and associative laws to solve problems in a range of contexts.

Lesson Summary

You will learn to explain how to use the factor pairs of 100 to solve calculations efficiently.

Key Notes

  • Scales are often marked in factors of 100
  • Rearranging calculations to make use of factors of 100 can simplify them

Vocabulary To Learn

  • Factor: Factors are whole numbers which exactly divide another whole number.
  • Commutative: The commutative law states that you can write the values of a calculation in a different order without changing the calculation; the result is the same. It applies for 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 for addition and multiplication.

Common Mistakes To Avoid

  • Pupils decompose the wrong factor therefore find it difficult to find a pair of factors that are equal to 100

3 Quick Questions (With Answers)

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

Scales are often marked in factors of 100. Rearranging calculations to make use of factors of 100 can simplify them.

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

Factors are whole numbers which exactly divide another whole number. Use this word when showing your method, then check your final answer is reasonable.

3. Spot and fix this common maths mistake.

Mistake: Pupils decompose the wrong factor therefore find it difficult to find a pair of factors that are equal to 100. Correction: Scaffold pupil's thinking when they begin to tackle a 2 digit by 2 digit calculation. Encourage them to ask questions of the numbers, for example: 'Is one of the numbers I have to start with a factor of 100?'.

More Lessons In This Unit

Browse all guides in the Year 5 Maths guide library.