IXL | Write equations for proportional relationships from graphs

Beth loves to wear socks with crazy patterns. She finds a great deal for these kinds of socks at her favorite store, Rock Those Socks.

There is a proportional relationship between the number of pairs of socks that Beth buys,

and the total cost (in dollars),

Write an equation for the relationship between x and

Simplify any fractions.

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Learn with an example

question

A mysterious flying superhero known as Blue Sky protects the good citizens of Silvergrove. Unknown to these citizens, Blue Sky is actually mild-mannered Bryan, a scientist in a flying suit. Before Bryan can fly in the suit, he needs to charge its battery.

There is a proportional relationship between the number of hours Bryan has charged his flying suit,

and the number of hours he can fly,

Write an equation for the relationship between x and

Simplify any fractions.

key idea

The graph of a proportional relationship is a straight line passing through the origin

(

)

A proportional relationship between x and y can be modeled by the equation

The letter k is the constant ratio of y to

It is called the constant of proportionality.

solution

To write an equation for the relationship between x and

first find the constant of proportionality. Start by identifying the coordinates of one of the points on the line.

Calculate the ratio of the

y-coordinate

to the

x-coordinate.

The constant of proportionality is 2 flight hours per hour charged.

The equation for the relationship is:

Looking for more? Try these:

Lesson: Proportional relationships

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Teacher tools

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Not feeling ready yet? These can help:

X.4Find the constant of proportionality from a graph

X.2Write equations for proportional relationships from tables

Lesson: Proportional relationships

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