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Year 2 - Maths

Use a number line to position and estimate the numbers 20-99

Counting and representing the numbers 20 to 99

Unit Summary

In this unit pupils will explore the counting sequence for counting to 100 and beyond representing numbers from 20-99 in different ways including marking the position on a number line They will learn to represent 20-99 in the context of length.

Lesson Summary

You will learn to position the numbers 20-99 on a number line including in the context of measures.

Key Notes

  • We can use the intervals on a number line to help us find and position other numbers.
  • The multiples of ten can help us find which decade a number is in.
  • The midpoint we refer to is halfway between each multiple of ten.
  • The midpoint we refer to has a ones digit of five.
  • The midpoint can help us position numbers that are not close to a multiple of ten.

Vocabulary To Learn

  • Midpoint: The middle of something. The point halfway along.
  • Previous: Going before in time or order.

Common Mistakes To Avoid

  • When finding the previous multiple of ten, children may misapply what they know about counting in tens. For example, they may think 30 is before 40, so think 30 is the multiple of ten before 45

3 Quick Questions (With Answers)

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

We can use the intervals on a number line to help us find and position other numbers. The multiples of ten can help us find which decade a number is in.

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

The middle of something. The point halfway along. Use this word when showing your method, then check your final answer is reasonable.

3. Spot and fix this common maths mistake.

Mistake: When finding the previous multiple of ten, children may misapply what they know about counting in tens. For example, they may think 30 is before 40, so think 30 is the multiple of ten before 45. Correction: Make deliberate errors to discuss and encourage children to visualise, then label, their own number lines marked in tens.

More Lessons In This Unit

Browse all guides in the Year 2 Maths guide library.