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### Course: 7th grade (Illustrative Mathematics)>Unit 2

Lesson 3: Lesson 4: Proportional relationships and equations

# Constant of proportionality from table (with equations)

Sal identifies the constant of proportionality from table.

## Want to join the conversation?

• so when your doing the table do you always times by 2.5
• You only use the constant of proportionality that is given in the table.It varies in each problem.
• I willl ask a question! Can this comment get to at least 1 real vote?
• yes bro I got you
• For a proportionality, do you always find the ratio from the left to the right, or in some cases do you find the ratio from right to left, and if you do, how do you know which direction you take the ratio from in a problem(left to right or right to left)
• so from left to right in most cases is is multiplication but right to left in most cases in division.
• he just took 2.5 out of nowhere like what
• It doesn't come out of nowhere. As Sal tells you in the video, you start with the value of "x" and you find the value that you can multiply with "x" to create the y-value.

Or, use the forumula: y=rx
If x=4 and y=10, plug in those values: 10=4r
Solve for "r" by dividing by 4: r = 10/4 = 2.5

Hope this helps.
• what if the numbers on the right are fractions
• By the right you mean Y, right?
Example:
If we have 1/3 as Y, and we have 2 as x, it might just be easier for you to divide the fractions/turn the fraction into a decimal, and then divide the Y by the X.

So with my example, 1/3

1/3 = 0.3 repeating

Then you would divide that by whatever X is.

So, in simple words, turn Y into a decimal first, and then divide Y by X.

Hope this helped!
If it did, can you pls give me a vote? :)
• I did the entire Unit 1................ my brain hurts
• My single braincell is fried
• thi is to hard for my tiny brain lol
• so basically, you have to find a specific number to solve for each problem with the same number?
• yes but that specific number is called the constant of proportionality and its what fits the entire question together