The connection with addition and subtraction (3rd grade math)

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.

This lesson is meant for 3rd grade math