Envision Math 2.0: Grade 8, Volume 1
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6. Sketch Functions from Verbal Descriptions
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Exercise 13 Page 200

Think of a real-life scenario where the amount of people in a place changes over time.

See solution.

Practice makes perfect

Let's take a look at the axes of the given coordinate plane.

Total people vs time coordinate plane
We begin by identifying the independent and dependent variables. Since Time is on the x-axis, it is the independent variable. Likewise, since Total People is on the y-axis, it is the dependent variable. Independent Variable:& Time Dependent Variable:& Total People

Next, we think of a scenario where the total number of people depends on the time. We are also given that this function must have at least two different intervals, so we might think of a place that fills up with people for some time and then empties out.

Total people vs time coordinate plane

Let's use a movie theater! People gradually come into the theater to take their seats before the movie begins. This is shown as a small interval where the function is increasing.

Total people vs time increasing interval

After the movie starts, everyone stays in their seats for the duration of the movie. This is represented by a longer interval where the function is constant.

Total people vs time increasing and constant intervals

After the movie ends, people start to leave the movie theater. This is shown as a small interval where the function is decreasing.

Total people vs time increasing, decreasing, and constant intervals

Note that this is just one example of a function describing a total number of people in a place as a function of time. We can also consider the number of people in a stadium, students in a classroom, or even users on a streaming service. The list goes on and on!