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Year 5 - Maths

Multiply a 3-digit by a 1-digit number with multiple regroups

Multiplication by partitioning leading to short multiplication (3 by 1-digit)

Unit Summary

In this unit pupils will multiply a 3-digit number by a single-digit number using expanded and short multiplication.

Lesson Summary

You will learn to multiply a 3-digit by a 1-digit number using expanded and short multiplication (multiple regroups).

Key Notes

  • If the product of the ones digits is greater than 10 then you regroup ten ones into one ten.
  • If the product of the 1-digit number and the tens digit is greater than 100 then you regroup ten 10s into one 100
  • If the product of the 1-digit number and the 100s digit is greater than 1,000 then you regroup ten 100s into one 1,000

Vocabulary To Learn

  • Short multiplication: A way of recording using columns to set out and calculate a multiplication.
  • Expanded multiplication: A way of recording the steps of a calculation focusing on partitioning one or more factors and showing partial products.
  • Regroup: The process of unitising and exchanging between place values is known as regrouping.

Common Mistakes To Avoid

  • Incorrectly regrouping or forgetting to record a regrouped amount.

3 Quick Questions (With Answers)

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

If the product of the ones digits is greater than 10 then you regroup ten ones into one ten. If the product of the 1-digit number and the tens digit is greater than 100 then you regroup ten 10s into one 100.

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

A way of recording using columns to set out and calculate a multiplication. Use this word when showing your method, then check your final answer is reasonable.

3. Spot and fix this common maths mistake.

Mistake: Incorrectly regrouping or forgetting to record a regrouped amount. Correction: Clear teacher modelling. 'What does this digit represent?' 'Where do we place the regrouped amount?'.

More Lessons In This Unit

Browse all guides in the Year 5 Maths guide library.