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Year 3 - Maths

Cross the hundreds boundary when adding and subtracting any 2-digit multiple of 10

Bridging 100: counting on and back in 10s, adding/subtracting multiples of 10

Unit Summary

In this unit pupils will find pairs of number that compose 100. They will position 3-digit numbers on a number line and estimate their position on unmarked number lines. They will compare and order 3-digit numbers.

Lesson Summary

You will learn to cross the 100s boundary when adding and subtracting multiples of ten.

Key Notes

  • When you add and subtract multiples of 10, the ones digit stays the same.
  • When you add and subtract multiples of 10, the tens digit and sometimes the 100s digit will change.
  • Number facts can help when adding and subtracting multiples of 10

Vocabulary To Learn

  • Multiple: The result of multiplying a number by another whole number.
  • 100s boundary: The point at which the numbers change into 100s numbers, or from one set of hundreds to another.

Common Mistakes To Avoid

  • Pupils may have difficultly partitioning 10s when crossing the 100s boundary. (e.g. 125 - 40)

3 Quick Questions (With Answers)

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

When you add and subtract multiples of 10, the ones digit stays the same. When you add and subtract multiples of 10, the tens digit and sometimes the 100s digit will change.

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

The result of multiplying a number by 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 may have difficultly partitioning 10s when crossing the 100s boundary. (e.g. 125 - 40). Correction: Pupils practice adding to/subtracting from multiples of 10 (e.g. 130 - 50) before exploring non-multiples of 10 (e.g. 85 + 30).

More Lessons In This Unit

Browse all guides in the Year 3 Maths guide library.