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# 1.11 Addition and subtraction: bridging 10

Created on 15 January 2018 by ncetm_administrator
Updated on 26 November 2018 by ncetm_administrator

## Introduction

Apply the aggregation and augmentation structures of addition to three single-digit numbers, exploring commutativity and associativity, to work towards strategies for adding and subtracting across ten.

## Teaching points

• Teaching point 1: Addition of three addends can be described by an aggregation story with three parts.

• Teaching point 2: Addition of three addends can be described by an augmentation story with a ‘first…, then…, then…, now…’ structure.

• Teaching point 3: The order in which addends (parts) are added or grouped does not change the sum (associative and commutative laws).

• Teaching point 4: When we are adding three numbers, we choose the most efficient order in which to add them, including identifying two addends that make ten (combining).

• Teaching point 5: We can add two numbers which bridge the tens boundary by using a ‘make ten’ strategy.

• Teaching point 6: We can subtract across the tens boundary by subtracting through ten or subtracting from ten.

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