For subtraction situations within 20, the learner can find the difference by starting at the number being subtracted and counting forward until reaching the starting quantity; the number of counts is the difference (for example, 13 − 8 is five counts from 8 to 13). A number line makes this relationship visible and connects subtraction to the inverse addition question, while distinguishing the number of steps from the endpoint; larger numbers and more general counting-up strategies are not included.
To solve a subtraction problem, start at the number you are subtracting. Count forward until you reach the first number. The number of steps you count is the answer.
Example: Find .
Start at .
Count forward to :
Count the steps:
There are steps, so:
This also shows the related addition fact:
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