IXL - Identify proportional relationships (Algebra 1 practice)

Look at this graph.

$10

Cost

Guests

Cost of Polly's birthday party

Is the total cost directly proportional to the number of guests?

yes

ref_doc_title.

Learn with an example

question

Look at this graph.

Paper recycled (kilograms)

Weeks

Total kilograms of paper recycled

Is the total amount of paper recycled proportional to the number of weeks on the new recycling plan?

yes

key idea

The graph of a proportional relationship is a straight line that passes through the origin.
Proportional quantities can be described by the equation y = kx, where k is a constant ratio.

solution

You can tell that the relationship is not directly proportional by looking at the graph. The graph is a straight line, but it does not pass through the origin. So, the relationship is not directly proportional.

You can also confirm that the linear relationship is not directly proportional by showing that the relationship cannot be written as y = kx, where k is a constant ratio.

First, create a chart. Use points from the graph, such as (1, 2) and (6, 9).

Paper recycled (kilograms) (y)	2	9
Weeks (x)	1	6

Now divide "Paper recycled (kilograms) (y)" by "Weeks (x)" to find the ratio (k).

Paper recycled (kilograms) (y)	2	9
Weeks (x)	1	6
Ratio (k)	2	1.5

The ratio (k) is not constant, so the relationship can't be described by the equation y = kx, where k is a constant ratio. This means that the relationship is not directly proportional.

Looking for more? Try these:

Lesson: Proportional relationships

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Teacher tools

Work it out

Not feeling ready yet? These can help:

X.6Identify proportional relationships from graphs and equations

X.7Identify proportional relationships from tables

Lesson: Proportional relationships

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