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Analyzing Graphs - Water Usage During a Typical Day at School

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Common Core For Algebra I

New York State Common Core Math Algebra I, Module 1, Lesson 4

Worksheets for Algebra I, Module 1, Lesson 4 (pdf)

Examples, solution, and videos to help Algebra I students develop the tools necessary to discern units for quantities in real-world situations and choose levels of accuracy appropriate to limitations on measurement. They refine their skills in interpreting the meaning of features appearing in graphs.


1. The bulk of water usage is due to the flushing of toilets. Each flush uses 2.5 gallons of water. Samson estimates that 2% of the school population uses the bathroom between 10:00 a.m. and 10:01 a.m. right before homeroom. What is a good estimate of the population of the school?

2. Samson then wonders this: If everyone at the school flushed a toilet at the same time, how much water would go down the drain (if the water-pressure of the system allowed)? Are we able to find an answer for Samson?

3. Estimation Exercise
• Make a guess as to how many toilets are at the school.
• Make a guess as to how many students are in the school, and what percentage of students might be using the bathroom at break times between classes, just before the start of school, and just after the end of school. Are there enough toilets for the count of students wishing to use them?
• Using the previous two considerations, estimate the number of students using the bathroom during the peak minute of each break.
• Assuming each flush uses 2.5 gallons of water, estimate the amount of water being used during the peak minute of each break.
• What time of day do these breaks occur? (If the school schedule varies, consider today’s schedule.)
• Draw a graph that could represent the water consumption in a typical school day of your school.

Exit Ticket

Suppose the researchers collecting data for water consumption during a typical school day collected data through the night too.

a. For the period between the time the last person leaves the building for the evening and the time of the arrival of the first person the next morning, how should the graph of water consumption appear?

b. Suppose the researchers see instead, from the time 1.21 a.m. onwards, the graph shows a horizontal line of constant value, 4. What might have happened during the night?

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