Main content

## 7th grade (Illustrative Mathematics)

### Unit 2: Lesson 2

Lesson 3: More about constant of proportionality# Constant of proportionality from tables

Identifying proportionality constants by looking at tables of values.

## Want to join the conversation?

- Hi! Here is some practice to help you succeed.

Which table has a proportionality of 3?

A

x y

1 2

2 3

3 4

4 5

B

x y

5 15

6 18

7 21

C

x y

1 5

3 15

5 25

Please upvote this so that others can practice too. If there are any problems, please notify me; I a just a learner like you.

Edit- Please do not read the comments until you answer the question. Have a good day!(35 votes)- if I'm allowed to answer its b if not then ill delete this right away(5 votes)

- i hate math. I know that's bad but is it ok even though i work?(8 votes)
- Math may be one of the hardest subjects ever because teachers teach the students the content poorly and It becomes hard and you will get confused and will forget about that content easily. A way to fix this problem is to keep trying. It maybe difficult but I promise it will help you in the future. You should always study if you can! Always be inquisitive and ask questions. We are a community and if you really need help with something, just ask us and we will help you solve these problems! Also, work you way up so you can do harder problems! If you follow these tips, I know you can succeed in math, get degrees and get a good job! I hope this helped!(27 votes)

- once i watch the videos and then i go to a lesson i cant do it can someone help me😅(11 votes)
- I would watch the videos again and more carefully this time. Focus on equations and key words that Mr. Khan says.(6 votes)

- is there an easy way to do these?(8 votes)
- Why is the constant of proportionality represented as variable “k”. Can it be some other letter? Please help.(2 votes)
- It's really just a convention that everyone uses. Why everyone started using it, I don't know, but you could
**technically**use any other letter.(3 votes)

- what is 19+50?(5 votes)
- The answer is 69.(4 votes)

- math is so boring(4 votes)
- math is boring to you and a few more

but it'll be use full like 2 + 4

I do math I've learned to love it

you should too cause there's so much of it

I'm 60% through world math

and all I'm doin is following the path

so please don't complain about this subject

you'll use it everyday and you'll learn much of it

so unless you want to be weird sit think

about constants of proportionality(2 votes)

- This stuff is easy how do you hate math! it's the best subject.(4 votes)
- because we can(1 vote)

- how do you do fractions(3 votes)
- wait can you summarize an explination for these problems because i really don't understand. im failing math..(2 votes)
- Some of the summary depends on what level of background information you know. If you have studied about linear relations and slopes and intercepts, then the explanation is simple. A proportional relation is a linear function which goes through the origin (0,0), so it has a slope and a y intercept of 0.

Without that background, you have to learn what a linear function is which will form a line on a graph. The slope is defined as the change in y/change in x which some people relate to "rise/run," but the formula is m = (y2-y1)/(x2-x1). So you can subtract any two y values and their corresponding x values to calculate the slope. The constant of proportionality is just the slope of a line that goes through the origin.(1 vote)

## Video transcript

- [Instructor] We are asked, Which table has a constant of proportionality
between y and x of 0.6? Pause this video and see
if you can figure that out. All right, so just as a reminder, the constant of proportionality
between y and x, one way to think about it is that y is equal to
some constant times x. Y is proportional to x. And this constant right over here is our constant of proportionality. So if that's going to be 0.6, so in our tables, or in the table that has a constant of proportionality of 0.6, y should be equal to 0.6 times x for every x,y pair. So let's look at these choices. So is seven 0.6 times four? Well, no, seven is larger than four. 0.6 times four would actually be 2.4, so this one is not gonna be, is definitely not going to have a constant of proportionality of 0.6. And in fact, this table, this isn't even a
proportional relationship. For this first one, I would have to multiply by 7/4. And then here I'm going
to be multiplying by 10/6, which is equivalent to 5/3. And here I'm multiplying by 13/8, so I'm not multiplying by
the same constant every time. So this isn't even a
proportional relationship. Now let's look at choice B. Well, to go from four to 2.4, that is. You would multiply by 0.6. But that's not enough for us to say that this is truly a
proportional relationship. It would have to be 0.6 in every scenario. So let's see. Nine times 0.6, yeah, that is 5.4. Nine times six is 54. But now this is nine times 6/10. It's 54 divided by 10, which is 5.4. And now let's see, 14 times six is 84. So 14 times 6/10 would indeed be 8.4. So this looks like our choice. And we can verify that
this would not be the case. Let's see, three, to get to two we would
be multiplying by 2/3. And then here, once again,
we're multiplying by 2/3. And then here, once again,
we're multiplying by 2/3. So this is actually describing
a proportional relationship, but our constant of
proportionality here is 2/3, which, if you tried to
express it as a decimal, it would be 0.6 repeating. 2/3 is equal to 0.6 repeating. And so it is proportional
but does not have this constant of proportionality. So we like our choice B.