Add two 3-digit numbers using adjusting strategies
Lesson details
Learning outcome
I can adjust a number to make an addition easier.
Key learning points
- If you adjust an addend you adjust the sum by the inverse.
- If you add 1 to an addend you must subtract 1 from the sum.
- If you subtract 1 from an addend you must add 1 to the sum.
- A number line can represent the adjusting strategy.
Keywords
Adjust - When you adjust you make a small change to a number. This is done to make a calculation easier to solve mentally.
Inverse - The inverse is the opposite or reverse operation. For example, subtraction is the inverse operation of addition.
Efficient - Working efficiently means finding a way to solve a problem quickly whilst also maintaining accuracy.
Common misconception
Many pupils will want to use a written method/algorithm immediately such as column method. This lesson is to support mental addition strategies.
Encourage the children to forget about using written procedures because they are inefficient when the addends are suited to adjustment. As class teacher, use adjustment and race the children desperate to use columns to see who is fastest!
Teacher tip
This strategy is shown with practical resources and jottings but the end goal is for the children be able to do it mentally so try to reduce such supports as quickly as possible.
Licence
Lesson video
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Prior knowledge starter quiz
6 Questions
Q1.Which of these numbers is closest to 10?
Q2.Which of these numbers is closest to a tens boundary?
Q3.Which of these numbers is closest to 100?
Q4.Which number is closest to a hundreds boundary?
Q5.Which of these number lines accurately represents 22 + 12 = 34 using partitioning to bridge?
Q6.Match the complements to 100
8
5
11
2
25
40
Assessment exit quiz
6 Questions
Q1.What is the inverse of subtract 4?
Q2.Which of these number lines represents using adjustment to find the total of 25 + 49?
Q3.Solve the following sum using adjustment. 360 + 499 =
Q4.Solve the following sum using adjustment. = 390 + 270
Q5.Solve the following sum by adjusting both addends. = 199 + 599
Q6.Solve the following sum using adjustment. 397 + 296 =
To help you plan your 3 maths lesson on: Add two 3-digit numbers using adjusting strategies, download all teaching resources for free and adapt to suit your pupils' needs...
To help you plan your 3 maths lesson on: Add two 3-digit numbers using adjusting strategies, download all teaching resources for free and adapt to suit your pupils' needs.
The starter quiz will activate and check your pupils' prior knowledge, with versions available both with and without answers in PDF format.
We use learning cycles to break down learning into key concepts or ideas linked to the learning outcome. Each learning cycle features explanations with checks for understanding and practice tasks with feedback. All of this is found in our slide decks, ready for you to download and edit. The practice tasks are also available as printable worksheets and some lessons have additional materials with extra material you might need for teaching the lesson.
The assessment exit quiz will test your pupils' understanding of the key learning points.
Our video is a tool for planning, showing how other teachers might teach the lesson, offering helpful tips, modelled explanations and inspiration for your own delivery in the classroom. Plus, you can set it as homework or revision for pupils and keep their learning on track by sharing an online pupil version of this lesson.
Explore more key stage 2 maths lessons from the Informal and mental strategies for adding and subtracting two 3-digit numbers unit, dive into the full primary maths curriculum, or learn more about lesson planning.