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# Equations for proportional relationships

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

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• 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
• where is the practice questions?
• how old is khan academy
• 14 years speaking 2022
• what is real life example of the equation y=1/20*x
• i do not understand
(1 vote)
• Proportional relationships are a fundamental concept in mathematics, and they are often represented by the equation y = kx, where k is the constant of proportionality. This equation states that two quantities, x and y, are directly proportional to each other, meaning that they change at the same rate. The constant of proportionality, k, is a numerical value that represents the factor by which y changes when x changes by one unit.

To write a proportional equation, you need to first identify the two quantities that are directly proportional to each other. For example, the distance traveled by a car is directly proportional to the time it has been traveling, and the amount of money you earn is directly proportional to the number of hours you work.

Once you have identified the two quantities, you can use the following steps to write the proportional equation:

Write the equation in the form y = kx.
Substitute the values of x and y for two corresponding values.
Solve for k.

For example, let's say that you know that the distance traveled by a car is directly proportional to the time it has been traveling. You also know that the car has traveled 100 miles in 2 hours. To write the proportional equation, you would first substitute these values into the equation y = kx:

100 = k(2)

Solving for k, you get:

k = 50

Therefore, the proportional equation that represents the relationship between the distance traveled by the car and the time it has been traveling is y = 50x. This equation means that the car travels 50 miles for every hour it is traveling.
• why does y over x require a five minute video I think it requires like half of that time.
• i have a question, how is 8/2 and 12/3 equal to 4
(1 vote)
• Just remember that when there is a fraction, it basically means you're dividing. So 8/2 is 8 divided by 2, which equals 4. 12/3 is 12 divided by 3, which equals 4.