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.

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See also

Connection between multiplication and division

Math Mammoth Grade 3 curriculum

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