Question

A driver on a highway with little traffic decides to use cruise control. She notices that she passes mile marker 47 when she turns the cruise control on. Thirty-six minutes later, she is just passing mile marker 86. Draw a graph to represent this situation and determine the driver's average speed in miles per hour.

Answer 1

Points (0, 47) and (36, 86) can be placed on the graph and a line drawn through them. That line will have slope (86-47)/(36-0) = 39/36 = 13/12.

At x=60, representing 1 hour on cruise control, the line will have a y-value of 112, indicating the driver has just passed mile marker 112, which is
  112 -47 = 65
miles from when cruise control was first turned on.

The driver's average speed is 65 miles per hour.