Year 2 - Maths
Add and subtract 1 to and from a 2-digit number crossing the tens boundary
Adding and subtracting ones and tens to and from 2-digit numbers
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Study Guides
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 add and subtract 1s and 10s from 2 digit numbers. They will use number facts to add/subtract a single-digit number to/from a 2-digit number. They will use a part-part-whole model to represent addition and subtraction.
Lesson Summary
You will learn to add and subtract one to and from a two-digit number crossing the tens boundary.
Key Notes
- Finding one more is the same as adding one; finding one less is the same as subtracting one.
- Numbers that are one more or one less than each other have a difference of one.
- When one is added to a number with a ones digit of 9, the next multiple of ten will be reached.
- When one is subtracted from a multiple of ten, the number reached will have a ones digit of 9
- When one ten is changed for ten ones, or ten ones for one ten, it is called regrouping.
Vocabulary To Learn
- One more: One more is when there is a greater amount by one or another item in the set.
- One less: One less is when there is a smaller value by one.
- Difference: The result of subtracting one number from another, How much one number differs from another.
- Decade: A group of ten numbers below one hundred, each with the same tens digit.
- Regroup: To exchange ten ones for one ten or one ten for ten ones in order to calculate more easily.
Common Mistakes To Avoid
- Children may have difficulty finding one less than a multiple of ten saying, for example, one less than 60 is 69.
3 Quick Questions (With Answers)
1. Solve this in steps: explain the method from this lesson and why each step matters.
Finding one more is the same as adding one; finding one less is the same as subtracting one. Numbers that are one more or one less than each other have a difference of one.
2. Use this key word in a maths sentence and explain it clearly. 'One more'
One more is when there is a greater amount by one or another item in the set. 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 have difficulty finding one less than a multiple of ten saying, for example, one less than 60 is 69. Correction: Refer to the order of the decades counting forwards and backwards and encourage visualisation of the decades on number lines and one hundred squares to support this. Help children to generalise about the number before a decade number ending in 9.
More Lessons In This Unit
- Add and subtract 10 to and from a 2-digit number. Study Guide
- Add and subtract one to or from a two-digit number within a decade Study Guide
- Add by bridging a multiple of ten Study Guide
- Add multiples of 10 to 2-digit numbers. Study Guide
- Find 10 more or less than a 2-digit number. Study Guide
- Partition 2-digit numbers in different ways Study Guide
- Subtract by bridging a multiple of ten Study Guide
- Subtract multiples of ten from 2-digit numbers Study Guide
- Use bridging to solve addition and subtraction problems Study Guide
- Use efficient strategies to solve problems Study Guide
- Use number bonds to 10 to add/subtract one-digit and two-digit numbers Study Guide
- Use number facts to add or subtract a one-digit number and a two-digit number. Study Guide
- Use number facts to solve addition and subtraction problems. Study Guide
- Use number facts to solve problems in measures and data contexts Study Guide
Browse all guides in the Year 2 Maths guide library.