Subtraction Using Models and Common Core

Today, we will do subtraction using the common core approach as well as models.  The chart below shows both methods.  In the first example 134 is subtracted from 385 using the common core approach.  As you can see, we first break down 385 and 134 into hundreds, tens and ones.  After we do this we subtract the hundreds, tens and ones of 134 from 385.  Finally, we add the remaining numbers for the final answer. 

A different approach which uses models makes more sense to some students.  It can also be used as we are first introducing the concept of subtraction.  In this approach a different symbol is chosen to represent the hundreds, tens and ones of a number.  In this example the number 385 is represented using these symbols, as you can see in the chart below.  Following this the student would cross out 1 square representing the hundred in 134, that is being subtracted from 385.  Next the student would cross out 3 tens representing the 30 in 134 and 4 ones representing the four in 134.  The student then counts the remaining symbols and adds them for the final answer.  We are fortunate to have many different approaches to solve a problem for different types of learners.  As the equations become more complicated one method may be favored over another by the student.

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