Year 2 - Maths
Count a large group of objects by counting tens and ones
Counting and representing the numbers 20 to 99
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This pupil-friendly study guide includes a unit summary, clear notes, common mistakes, and quick questions with answers.
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 count larger groups of objects efficiently using tens and ones to help you.
Key Notes
- One item can be used to represent several other items. This is called unitising.
- The order in which tens and ones are arranged does not affect the value of the number.
- We can use a one hundred square to help find the value of two-digit numbers more efficiently.
Vocabulary To Learn
- Unitising: Unitising means treating groups that contain, or represent, the same number of things as 'ones' or 'units'. It is important in understanding place value and supports us to think multiplicatively.
Common Mistakes To Avoid
- Children may continue counting in tens when they reach the ones, e.g. count 2 tens and 3 ones completely in tens. They may think arrangement of tens and ones affects how to count them.
3 Quick Questions (With Answers)
1. Solve this in steps: explain the method from this lesson and why each step matters.
One item can be used to represent several other items. This is called unitising. The order in which tens and ones are arranged does not affect the value of the number.
2. Use this key word in a maths sentence and explain it clearly. 'Unitising'
Unitising means treating groups that contain, or represent, the same number of things as 'ones' or 'units'. It is important in understanding place value and supports us to think multiplicatively. Use this word when showing your method, then check your final answer is reasonable.
3. Spot and fix this common maths mistake.
Mistake: Children may continue counting in tens when they reach the ones, e.g. count 2 tens and 3 ones completely in tens. They may think arrangement of tens and ones affects how to count them. Correction: Make deliberate errors to prompt discussion and refer back to previous stem sentences, e.g. 'The objects are in ones, so I can count them in ones.' Present tens and ones in non-standard arrangements, so children practise always counting tens first.
More Lessons In This Unit
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