IXL | Write equations for proportional relationships from tables

Beth loves to bake blueberry muffins for her friends and family.

There is a proportional relationship between the volume of flour Beth uses (in cups),

and the number of muffins she bakes,

x (cups)	y (muffins)
1.5	9
2	12
2.5	15
3	18

Write an equation for the relationship between x and

Simplify any fractions.

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Learn with an example

question

There's a huge sale at the grocery store, so Brody stocks up on his favorite breakfast cereal, Frosted Crunchy Bunches. As he puts the cereal boxes on a shelf in his pantry, he wonders if he has enough shelf space.

There is a proportional relationship between the number of cereal boxes Brody stores on his pantry shelf,

and the amount of shelf space (in inches) the boxes take up,

x (boxes)	y (inches)
2	6.8
3	10.2
4	13.6
5	17

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 (boxes)	y (inches)	Ratio of y to x (inches per box)
2	6.8	6.8 2 = 3.4
3	10.2	10.2 3 = 3.4
4	13.6	13.6 4 = 3.4
5	17	17 5 = 3.4

The ratio for each pair of

and

y-values

3.4.

So, the variables have a proportional relationship.

So, the constant of proportionality is 3.4 inches per box.

The equation for the relationship is:

3.4

Looking for more? Try these:

Lesson: Proportional relationships

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N.1Find the constant of proportionality from a table

Lesson: Proportional relationships

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