If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

### Course: 7th grade (Illustrative Mathematics)>Unit 2

Lesson 9: Lesson 11: Interpreting graphs of proportional relationships

# Constant of proportionality from graph

In this lesson, we learn about the constant of proportionality in a graph. It's the number we multiply by x to get y. In our example, when x increases, y increases three times as much. So, our constant of proportionality is 3.

## Want to join the conversation?

• I'm confused in the constant proportionality and the way you set it up
• The constant of proportionality is the ratio between two directly proportional quantities. Two quantities are directly proportional when they increase and decrease at the same rate.
The constant of proportionality k is given by k=y/x where y and x are two quantities that are directly proportional to each other. Once you know the constant of proportionality you can find an equation representing the directly proportional relationship between x and y, namely y=kx, with your specific k.
Hope this helps!
• This is so confusing and it makes me very mad
• Hey, don't worry. Everyone has their least favorite subjects. If you look at the comment above, they explain how to find it. There is also another equation, but thats for later.
• Am i the only one who looks at the comments lol
• no you are not
• i hate life :)
• at this point me too 😁
• Thanks khan you're better than my math teacher
• Poor math teacher XDD
• noob here
• why is school so boring
• it’s because its a feature for the matrix
• This is a bit confusing I still don’t get it
• So, Y (the up and down part of the graph) equals K (The constant of proportionality, you get it by dividing Y by X), times X (the side by side part of the graph.)

This would equal= Y=KX

Then you look for a clear place where you can place a point, (I would recommend using graph paper for this) say, (4,8) and then you take the Y (X,Y) which is 8 and divide it by the X, which is 4 to get 2.

So, K=2.

Now lets check it.

8=2(4)
8=8