IXL | Constant rate of change: graphs

On Saturday, Liam noticed a sprout had emerged from his garden. Each day since, he has been measuring its growth.

There is a linear relationship between the time, in days, since Liam's first observation, and the height of the sprout, in centimeters.

Describe the rate of change for this relationship.

The height of the sprout by per day.

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Learn with an example

question

Tracy is on a cross-country road trip! She stops at a rest station to fill her gas tank and plans to drive for another 6 hours along the highway before making her next stop.

There is a linear relationship between the time, in hours, since Tracy filled the car with gas, and the amount of gas left the tank, in gallons.

Describe the rate of change for this relationship.

The amount of gas left by per hour.

key idea

You can use this formula to calculate the rate of change for a linear relationship between two variables,

and

rate of change

change in

solution

There is a linear relationship between the time, in hours,

since Tracy filled the car with gas, and the amount of gas left in the tank, in gallons,

You can use this formula to calculate the rate of change in gallons per hour:

rate of change

change in amount of gas left

change in time

First, identify two points on the line.

Find the change in the

-coordinates

from

(

)

and

(

)

This is the change in the amount of gas left.

–

Find the change in the

-coordinates.

This is the change in the time.

–

Divide to find the rate of change.

–

gallons per hour

Notice that the rate of change is

negative.

Also notice that the line on the graph goes down as it goes from left to right. Both observations indicate that as the time since Tracy filled her gas tank increases, the amount of gas left in the tank

decreases.

This sentence describes the rate of change for this relationship:

The amount of gas in the tank decreases by

per hour.

Looking for more? Try these:

Lesson: Slope

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Questions
answeredQuestions

Time
elapsedTime

hr	min	sec
00	00	04

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Teacher tools

Work it out

Not feeling ready yet? These can help:

MM.7Complete a table from a graph

B.24Add, subtract, multiply, and divide integers

L.5Unit rates

Lesson: Slope

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