# Ice Cream in Winter - Do Sales Increase or Decrease?

By Susan LoFranco on Apr 24, 2017

• Student will interpret whether data seems to be rising or falling
• Use a straight object to estimate a line through a linear system of points (rubber band, wikki stix, etc)

Note to Teachers:  This lesson will be followed by a lesson on slope (Ice Cream Sales on the Slope) which will expand on the same information. If doing this lesson save all the student data for this future lesson.

• Understand how to graph points and read coordinate graphs

## Materials

• Graph paper (raised and/or bold lined)
• Dots or other tactile material to place marks on graph points
• Colored markers indicating graph points
• String, rubber band, wikki stix, tape or other tactile material to make line of best fit
• Ice Cream vs. Temperature Worksheet
• Scatter Plot for Ice Cream vs. Temperature Template (for transfer onto graph paper)

## Procedure

Vocabulary: x-axis, y-axis, line of best fit (or trend line), interpolation (find a value inside a set of data points).

• With student review reasons for using a scatter plot (to determine if there is a cause and effect relationship).  Then review together data on Ice Cream Sales vs. Temperature Chart.
• Based on the way the data is presented in the Ice Cream Sales vs. Temperature Chart ask the student if it is easy to see a pattern.  (the response should be no).
• Review the Scatter Plot Ice Cream Vs. Temperature Chart (which should have been transferred to graph paper).  With the student, using either dots, markers or other tactile material plot the first two points where the temparateure and sales meet.
• If the student is confident let him/her continue until all the points are plotted.
• At this point the chart should show an upward trend.  Ask the student if it is easier to observe the pattern than by looking at the Ice Cream Sales vd. Temperature Chart and to describe the pattern.
• Once the pattern has been identified by the student have the student estimate a line through the date (using either wikki stix, tape, or other tactile material). This is the "Line of Best Fit" or "Trend Line".  It should be drawn as close as possible to all points, with as many points above the line as below.  The line should extend through to the end of the last data point.
• This "Line of Best Fit" can be used to identify values not named within the data set (interpolation) (eg. What will sales be if the temperature is 700?).    Have the student explore and record different values using the students media of choice.