IXL | Write equations for proportional relationships from tables: with decimals

The Unruly Queens chess club is hosting a tournament, and each club member is bringing something to eat or drink. Rosanne decides to bring oatmeal raisin cookies from her favorite bakery.

There is a proportional relationship between the number of oatmeal raisin cookies Rosanne buys,

and their total cost (in dollars),

x (cookies)	y (dollars)
6	$9.90
8	$13.20
10	$16.50
12	$19.80

Write an equation for the relationship between x and

Simplify any fractions.

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Learn with an example

question

Joey is throwing a pool party to kick off the summer. His pool is empty, so he starts filling it with water from a garden hose.

There is a proportional relationship between the time Joey has been filling up the pool (in minutes),

and the volume of water in the pool (in gallons),

x (minutes)	y (gallons)
0.5	10
0.8	16
0.9	18
1	20

Write an equation for the relationship between x and

Simplify any fractions.

key idea

Two variables have a proportional relationship if the ratio of one variable to the other is constant.

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. Calculate the ratio of y to

x (minutes)	y (gallons)	Ratio of y to x (gallons per minute)
0.5	10	10 0.5 = 20
0.8	16	16 0.8 = 20
0.9	18	18 0.9 = 20
1	20	20 1 = 20

The ratio for each pair of

and

y-values

20.

So, the variables have a proportional relationship.

So, the constant of proportionality is 20 gallons per minute.

The equation for the relationship is:

Looking for more? Try these:

Lesson: Proportional relationships

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