Subtraction Models
3 ways of working the same subtraction problem are demonstrated: comparison, take-away, and missing addend (or adding up).
Trade First
A method for multi-digit subtraction where we consider the differences in each place value and make necessary trades first, so we have enough to subtract from. Then we carry out the subtraction.
Partial Differences
A method for multi-digit subtraction where we subtract in each place value and record the difference. If we are subtracting more than we have, we use the notation of missing or lacking the overage amount. Then we combine the partial differences to obtain the final answer.
Compensation
We change the amount we are subtracting to a friendly number (or multiple of 10), by adding the same amount to both numbers in the subtraction sentence. This makes the subtraction easier to calculate in our heads.
Adding Up On An Open Number Line
This method shows that subtraction may be thought of as adding up. Demonstration of what we are thinking is done on an open number line. We make use of friendly numbers (multiples of 10) and jumping by tens to obtain the final answer.
Take Away On An Open Number Line
This method shows how to do subtraction by taking away a given amount on an open number line. We make use of friendly numbers (multiples of 10) and jumping by tens to obtain the final answer.
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