# Lesson overview:Thinking flexibly

- In this lesson, we will learn to think flexibly, looking for the most efficient strategies we can find for subtraction.

## Core Content

- In this lesson, we will learn to think flexibly, looking for the most efficient strategies we can find for subtraction.

## Extending calculation strategies and additive reasoning:

- Adjusting addends
- Same sum' with larger numbers
- Same sum' with decimals
- Balancing equations using the 'same sum' strategy
- Balancing equations using compensation
- Balancing equations: Does the order of addends matter?
- Increasing an addend
- Decreasing an addend
- Solve calculations mentally by relating them to known facts
- Find an unknown addend
- Introduction to same difference
- Same difference in context
- Use the Language of Minuend, Subtrahend, and Difference
- Transform calculations using the same difference
- Practice: Transforming Calculations to Make Them Easier to Solve Mentally
- Transform a subtraction calculation to make the written algorithm easier to apply
- Practice: 'Same Difference' in Different Contexts
- Balancing equations to find unknown values
- Explore how the difference changes when only the Minuend is changed
- Apply the generalisation about how the minuend and difference change to solve problems
- Explore how the generalisation can be used as a mental calculation strategy using Known facts
- Thinking flexibly
- Comparing Strategies
- The more we subtract, the less we are left with. The less we subtract...
- Contexts where the Minuend is Kept the Same, and the Subtrahend Increases
- Contexts where the minuend is kept the same, and the Subtrahend decreases
- Further practice to reason about how the change in the subtrahend changes the difference
- Explore problems in which the new difference must be found
- Balance Equations Where the Compensation Property of Same Sum Cannot Efficiently be Applied
- Balance Equations Where the Compensation Property of Same Difference Cannot Efficiently be Applied