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Properties of Proportional Graphs

• All graphs that represent a proportional relationship must be a straight line (linear)

• Proportional relationships must also show the line passing through the origin (0,0)

• The point on the graph (1, r) is the unit rate which is also constant of proportionality (k).

Identifying Unit Rate and K from a Graph

• The point on the graph (1, r), where r represents the unit rate, is also constant of proportionality (k).

This is an example of a graph with a line that is proportional. The constant of proportionality is 5. You can find the constant of proportionality by dividing one of the time values by the water values.

This is another example of a proportional relationship on a graph. The line goes through the origin (0, 0) and is a straight line. The constant of proportionality would be 50. In the context of the problem it takes 1 hour to get a total cost of $50.

This is an example of a non proportional relationship. In this situation, the line is a straight line, however the line does not cross the origin (0, 0).

Identifying Unit Rate and K from a Graph

Describing the Meaning of Unit Rate from a Graph

• Unit rate and the constant of proportionality describe the relationship between two quantities.

• This graph shows k=10/5 so k=2.

• The graph shows, for every 1 text message sent, we are charged $2.00!