# Proportional relationship between x and y

### Difference Between Proportional & Linear Relationships | Sciencing

On the graph of a proportional relationship, the constant of proportionality is the constant ratio of y to x, or the slope of the line. A proportional. If the relationship between “x” and “y” is proportional, it means that as “x” changes , “y” changes by the same percentage. Therefore, if “x” grows. Practice telling whether or not the relationship between two quantities is proportional by looking at a table of the relationship.

- 7.2.1 Proportional Relationships
- Graphing proportional relationships: unit rate
- Proportional relationships: graphs

And let's say that when x is one, y is three, and then when x is two, y is six. And when x is nine, y is Now this is a proportional relationship. Because the ratio between y and x is always the same thing. And actually the ratio between y and x or, you could say the ratio between x and y, is always the same thing.

So, for example-- if we say the ratio y 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 y over x 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 a proportional relationship between y and x.

So this one right over here is proportional. So given that, what's an example of relationships that are not proportional.

### Proportional relationships: graphs (video) | Khan Academy

Well those are fairly easy to construct. So let's say we had-- I'll do it with two different variables. So if this is the point 0, 0, this should be on my line right over there. Now, let's think about what happens as we increase x.

So if x goes from 0 to 1, we already know that a change of 1 unit in x corresponds to a change of 0. So if x increases by 1, then y is going to increase by 0. It's not so easy to graph this 1 comma 0.

So let's try to get this to be a whole number. So then when x increases another 1, y is going to increase by 0.

**Directly and Inversely Proportional Relationships**

It's going to get to 0. When x increases again by 1, then y is going to increase by 0. It's going to get to 1. If x increases again, y is going to increase by 0. So just to 1. Notice, every time x is increasing by 1, y is increasing by 0. That's exactly what they told us here. Now, if x increases by 1 again to 5, then y is going to increase 0. And I like this point because this is nice and easy to graph.

So we see that the point 0, 0 and the point 5 comma 2 should be on this graph. And I could draw it. And I'm going to do it on the tool in a second as well.

Students mistakenly think slope is only found on graphs, but slope is a way of describing a constant rate of change that can be graphical, tabular, or symbolic.

Sometimes students are plotting points incorrectly, switching around the x and y coordinates, or not including the negative sign if there is a negative coordinate.

### Proportionality (mathematics) - Wikipedia

Thinking products are always greater than factors ex. Thinking that all relationships that increase or decrease by a constant value are proportional. If students are unclear about what they are dividing or what they are trying to find out, they often can get a constant that is not appropriate; they could be satisfied just getting an answer and moving on, not testing the reasonableness of their answer. Today you can see the 10 stacks of different books I have at the front of the room.

Each group gets one set of 10 of the same kind of book. Do not use magazines, or if you do, use that as an added topic after the activity is over.

## Intro to proportional relationships

If I told you how many of your books are in a stack, can you tell me the height? Or, if I told you the height of your stack of books, can you tell me how many books are in the stack? Your group's task is to find out how tall different stacks of books are.

You will need to make a two-column table for number of books and height of the stack. Count from 0 to ten for the number of books. The independent variable will be what? What do we already know? The number of books is the independent variable because the height of the stack depends on the number of books. So height is my dependent variable.

Make sure your table starts at 0 books. Your task is to use the same type of book and figure out what different stacks' heights are.

Do not take any shortcuts here. I want to know the height of each of the 10 stacks of books. The teacher is walking around the room questioning and assisting groups of working students. Tell me about that. Then we took 2 books and measured how tall those books were. We are going to keep going until we have 10 books' height. Students to one another in their group: Maybe we're doing it wrong?

## Proportionality (mathematics)

How can this be? If one book is 3. How about we re-measure, and this time let's have the same person measure, ok? Teacher walks around the room. After some time, she hears the following: Why do you think that would work?

Well, each book is the same height as the others, so we can just multiply.

Wow, that is easy! So by actually doing the activity and thinking through it, you have solved the problem. Like 1 book was 2. Our table doesn't change by exactly the same value, but our graph is almost a perfectly straight line going up. Where does your graph start? Who else graphed this? What can we conclude then about our graphs?