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.

Lesson 6: Equations of proportional relationships

# Equations for proportional relationships

Learn how to write a proportional equation y=kx where k is the so-called "constant of proportionality".

## Want to join the conversation?

• So I am doing the practice problems for this right now and sometimes the constant of proportionality is a fraction, like "y=1/3x" but sometimes it is a number or a decimal, like "y=0.34x" or "y=4x". How do I know which one to do? There have been multiple times where I put the decimal equal to the fraction, like 0.33 for 1/3 and gotten it wrong because it was supposed to be the fraction (and vice versa)
• I have experienced similar issues entering answers. After doing quite a few of these types of problems, I have found that entering your answer as a fraction is the safer bet, especially when your answer is something like 10/7x=y as 10/7 is a repeating decimal. I enter the answer as a decimal only if the question prompts me to do something like "round my answer to the nearest hundredth." Then I obviously know my answer should have a decimal in it. Otherwise, I just seem to run into problems with entering them usually do to rounding.

So yeah, I just feel that it is better to answer these kinds of questions with a fraction instead of the decimal unless you are specifically told to do so in the question.
• i dont understand this
• what he is trying to say when 4 and 1 I think they mean the unit rate is 4 or it can 4/1
• how old is khan academy
• 14 years speaking 2022
• So I am doing the practice problems for this right now and sometimes the constant of proportionality is a fraction, like "y=1/3x" but sometimes it is a number or a decimal, like "y=0.34x" or "y=4x". How do I know which one to do? There have been multiple times where I put the decimal equal to the fraction, like 0.33 for 1/3 and gotten it wrong because it was supposed to be the fraction (and vice versa)I have experienced similar issues entering answers. After doing quite a few of these types of problems, I have found that entering your answer as a fraction is the safer bet, especially when your answer is something like 10/7x=y as 10/7 is a repeating decimal. I enter the answer as a decimal only if the question prompts me to do something like "round my answer to the nearest hundredth." Then I obviously know my answer should have a decimal in it. Otherwise, I just seem to run into problems with entering them usually do to rounding.

So yeah, I just feel that it is better to answer these kinds of questions with a fraction instead of the decimal unless you are specifically told to
• ?? does this mean in real life ?_?
(1 vote)
• what is real life example of the equation y=1/20*x
• I'm i bit confused with this. Can someone pls help me? I would really appreciate it. 💖💖
• Hi IsabH! The first step to proportional relationships is knowing how to find the constant of proportionality. The formula is "y=xk" with "k" being the constant. To solve for "k", you can divide "y" by "x". In the video, Sal also solves for the rate. The rate is actually the same thing as the constant of proportionality. A rate is also known as a unit rate. The equations for proportional relationships are "y=xk" and "y/x=k". Hope this helps. Have a great day! 😄
• where is the practice questions?