The Postal-Scale Function

In an Algebra 2 book, Shelby, Katy, and Don found the problem of finding the function which describes the cost of sending a letter by USPS 1st class mail. Don found the scale which he uses, shown below.  Katy made a table

  weight (oz)    0-1      1-2     2-3       3-4

  cost($)            .39       .63     .87      1.11

The interesting thing is that any # of ounces between 0-1, including 1, the cost is $.39; between 1-2 ounces, the cost is $.63. They discovered that after $.39 for 1 ounce, the cost goes up the same,  $.24. So if the weight was 1.25 ounces or 1.8 ounces, the cost would be the same, $.63. In the book "Mathematica 5" by Stephen Wolfram, Don found the name of this function, the ceiling function. The ceiling of x is written as .

Shelby and Katy made the graph and wrote the equation.

The graph of the USPS cost ($) vs. weight (oz) of a letter

Great job, Katy and Shelby!!!