Introduction to proportional relationships 7 th grade Khan Academy

What want to introduce you to in this video is the notion of proportional relationship. And proportional relationship between two variables is just relationship where the ratio between the two variables is always going to be the same thing. So let's look at an example of that. So let's just say that we want to think about the relationship between and And let's say that when is one, is three, and then when is two, is six. And when is nine, is 27. Now this is proportional relationship. Why is that? Because the ratio between and is always the same thing. And actually the ratio between and or, you could say the ratio between and is always the same thing. So, for example-- if we say the ratio over x-- this is always equal to-- it could be three over one, which is just three. It could be six over two, which is also just three. It could be 27 over nine, which is also just three. So you see that over is always going to be equal to three, or at least in this table right over here. And so, or at least based on the data points we have just seen. So based on this, it looks like that we have proportional relationship between and So this one right over here is proportional. So given that, what's an example of relationships that are not proportional. Well those are fairly easy to construct. So let's say we had-- I'll do it with two different variables. So let's say we have and And let's say when is one, is three. And when is two, is six. And when is 10, is 35. So here-- you might say look, look when is one, is three so the ratio to a-- you could say to a-- you could say well when is three, is one. Or when is one, is three. So three to one. And that's also the case when is six, is two. Or when is two, is six. So it's six to two. So these ratios seem to be the same. They're both three. But then all of sudden the ratio is different right over here. This is not equal to 35 over 10. So this is not proportional relationship. In order to be proportional the ratio between the two variables always has to be the same. So this right over here-- This is not proportional. Not proportional. So the key in identifying proportional relationship is look at the different values that the variables take on when one variable is one value, and then what is the other variable become? And then take the ratio between them. Here we took the ratio to and you see to or divided by x-- the ratio of to is always going to be the same here so this is proportional. And you could actually gone the other way. You could have said, well what's the ratio of to Well over here it would be one to three, which is the same thing as two to six, which is the same thing as nine to 27. When you take this ratio-- if you say the ratio of to instead of to you see that it is always one third. But any way you look at it-- the ratio between these two variables-- if you say to it's always going to be three. Or to is always going to be one third. So this is proportional while this one is not.