1. Proportional vs. Non-proportional
Thursday, April 27, 2017

2. Review Key Vocabulary
Proportional – when two quantities that simplify to the same ratio.
Constant – a quantity having a value that does not change or vary.
Constant of Proportionality - a constant value of the ratio of two proportional quantities.

3. Proportionality
Two quantities are directly proportional if they have a constant ratio
The change in one variable is always accompanied by a change in the other.
This constant ratio is called the “constant of proportionality”. The constant of proportionality can never be zero.

4. Proportional Relationships
Identify the constant of proportionality:
The constant of proportionality is the unit rate
From the table, look at the ratio of y to x
From the graph, look at the steepness of the graph or look for the y-value where x is one
From the equation, look for the coefficient of x

5. Proportional vs. Non-Proportional
Two quantities are directly proportional if they have a constant ratio
If the ratio is not constant, the two quantities are non-proportional.
We will look at tables, graphs, equations, and ordered pairs to determine if the relationship between the variables is proportional.

6. Equations:
You should also be able to write equations to describe the relationships.
If the situation is proportional, you will use your constant of proportionality in your equation.
Be sure to define your variables!!!

7. Proportional relationships: tables
In order to tell from a table if there is a proportional relationship between the variables, you should check to see if the ratio is the same for all values in the table.
The ratio is also known as the scale factor.
Reduce or divide to find the constant of proportionality (unit rate) that defines the relationship between the variables.

8. Determine if the tables below represent a proportional relationship.
Pounds (x)
Cost (y) 4 $1 6
$1.50 8 $2 10
$2.50
Number of books (x)
Price (y) 1 3 9 4 12 7 18
Proportional? ________
Ratio __________
Equation ___________
Const of Prop __________
Proportional? ________
Ratio __________
Equation ___________
Const of Prop __________

9. Proportional? ________
Ratio __________
Equation ___________
Const of Prop __________

10. Proportional? ________
Ratio __________
Equation ___________
Const of Prop __________

11. Proportional? ________
Ratio __________
Equation ___________
Const of Prop __________

12. Proportional Relationships: graphs
The graph of a proportion will always be a straight line that passes through the origin (0,0).
Always write the constant ratio in the form of

13. LearnZillion Notes:
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14. Determine if the graphs below represent a proportional relationship.
Why?
Line goes thru the origin
Why?
Line does not
go thru the origin

15. How does the average speed from hour 1 to hour 4 compare to the average speed from hour 5 to hour 6? One way to estimate between which pair of coordinates the average speed was greater is to look at the graph and see where the rate of change, or change in miles per change in hours was greater, which would subsequently make the line graph steeper. The line segment between hour 5 and 6 appears to be steeper to me than the line segment between hour 1 and 4, but to make sure, let’s find the precise average speed between each pair of coordinates.

16. How does the average speed from hour 1 to hour 4 compare to the average speed from hour 5 to hour 6? One way to estimate between which pair of coordinates the average speed was greater is to look at the graph and see where the rate of change, or change in miles per change in hours was greater, which would subsequently make the line graph steeper. The line segment between hour 5 and 6 appears to be steeper to me than the line segment between hour 1 and 4, but to make sure, let’s find the precise average speed between each pair of coordinates.

17. Proportional?
How can You determine the unit rate from a graph?
Constant of proportionality?
Equation?

18. Proportional?
How can You determine the unit rate from a graph?
Constant of proportionality?
Equation?

19. Proportional?
How can You determine the unit rate from a graph?
Constant of proportionality?
Equation?

20. Proportional relationships: equations
Determine if the following equations show a
proportional relationship.
Substitute a zero for x in the equation and then solve.
If y then equals zero, then the equation represents a
proportional relationship because the graph of the line
goes through the origin.
y = 3x – 1
y = 10x