^

We look at simple bar models with one unknown part, and write simple addition & subtraction equations matching the bar model. For example:

```
<-------750----------->
|------|--------------|
218         ?
```

We can write an addition equation:

218 + ? = 750

... and we can write two subtractions:

750 − 218 = ?
750 − ? = 218

After this we review the concept of difference, and find the difference between two numbers in two ways: by subtracting, and by adding up (which demonstrates how addition and subtraction are related).

Lastly it's time for some word problems.

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Connection between multiplication and division

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