Example 2

In 2008, about 66 million U.S. households had both landline phones and cell phones. This number decreased by an average of 5 million households per year. Use the table below to calculate the rate of change for the interval [2008, 2011].
  1. Determine the interval to be observed.
  2. Determine .
  3. Determine .
  4. Substitute ) and into the slope formula to calculate the rate of change.
This applet is provided by Walch Education as supplemental material for their mathematics programs. Visit www.walch.com for more information on their resources.