Carlos gets to class at 9:08 a.m. He has to write down homework assignments and complete morning work before math begins at 9:30 a.m.
How many minutes does Carlos have to complete his tasks before math begins?
Use your number line template to label the points when Carlos arrives and when math starts.
Writing down homework assignments is the first thing Carlos does when he gets to class. It takes 4 minutes. Plot the point that shows when Carlos finishes this first task.
At what time did you plot the point? 9:12 a.m.
What does the interval between 9:12 and 9:30 represent?
The number of minutes it takes Carlos to finish his morning work.
How can we find the number of minutes it takes Carlos to complete morning work?
Count on the number line. Count forward from 9:12 to 9:30.
What addition sentence represents this problem?
12 minutes + ____ = 30 minutes.
Find the number of minutes it takes Carlos to complete morning work.
How many minutes did it take Carlos to finish morning work? 18 minutes.
How could we have modeled that problem by counting backward?
We could have started at 9:30 and counted back until we got to 9:12.
What subtraction sentence represents this problem?
30 minutes – 12 minutes = 18 minutes.
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