Posted by lyndse on Saturday, December 12, 2009 at 1:37pm.
For which values is the relationship linear? Tell how you decided. Write the equation for each linear relationship
x 5 10 15 20 25 30
y 20 30 40 50 50 50

Math  drwls, Saturday, December 12, 2009 at 2:07pm
It is linear from x = 5 to x = 20 because the ratio of the change in y to the change in x is a constant over that interval. There is a different linear relationship (y = constant)for 20<x<30.
The slope is discontinuous at x=20. Two linear lines join there (if you were to plot a graph). 
Math  lyndse, Saturday, December 12, 2009 at 3:01pm
I still can't quite grasp it but your explanation is very helpful. Thank you!