IXL | Write and solve equations for proportional relationships

Read the description of a proportional relationship.

Fascinated by ocean life, Carmen wants to put a saltwater aquarium in her bedroom. She needs to make sure she buys a big enough tank to grow her collection of fish over time. There is a proportional relationship between the number of

fish

in Carmen's collection,

, and the smallest tank size (in

gallons

, she needs to safely keep her fish.

For 2

fish,

Carmen needs a 10 gallon tank. Write the equation for the relationship between x and

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Learn with an example

question

Read the description of a proportional relationship.

Sean is determining the number of quarters equal to different dollar amounts. There is a proportional relationship between the amount of money in

dollars

, and the number of

quarters

$1 is equal to 4

quarters.

Write the equation for the relationship between x and

key idea

A proportional relationship between x and y can be modeled by y =

kx.

In this equation, k is the constant ratio of y to

It is called the constant of

proportionality.

solution

There is a proportional relationship between the amount of money in

dollars,

and the number of

quarters,

To write the equation for this relationship, find

Use the numbers given in the problem and their units.

$1 is equal to 4

quarters.

When the

x-value

is 1, the

y-value

is 4. Now calculate

the ratio of y to

Plug k = 4 into the equation y = kx to find the equation for this relationship.

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:

S.11Unit rates

AA.16Write a one-step equation: word problems

AA.9Solve one-step multiplication and division equations with whole numbers

Lesson: Proportional relationships

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