Ice Cream In Winter - The Slope

By Susan LoFranco on Apr 24, 2017

  • Given a linear set of points where the x coordinates increase by one, identify what the y coordinates are increasing by as a rate of prices rising or falling.  

This lesson connects to a previous lesson "Ice Cream in Winter - Do Sales Increase or Decrease?"  The student will need to have completed that lesson in order to calculate slope in this lesson. 

• Nemeth: understanding of a table of values as a way to represent multiple points and understanding of how to graph the points in a coordinate system, Delta symbol (meaning change), and subscript.


  • Graph paper
  • Dots, markers, Wikki Stix or other tactile method of conntecting coordinates
  • You Tube Video which gives about a 4 minute explanation of calculating slope
  • You Tube Video - Slope Dude - gives a verbal description of positive slope, negative slope, and undefined.
  • Slope Dude Worksheet for student to follow along with the Slope Dude Video

scatter plot for ice cream vs. temperaturescatter plot for ice cream vs. temperature part 2


Vocabulary: Slope, Variables, Coordinates, Line of Best Fit, x-axis, y-axis

The graph created in the lesson "Ice Cream in Winter - Do Sales Increase or Decrease?" which has a Line of Best Fit will be used to calculate the value of the slope in this lesson.

  • Review with the student the definition of 'slope'.   Using the YouTube Video "Slope Dude" and the Slope Dude pdf listen to the description of what slope does.  Slope can be positve (increasing), negative (decreasing) or undefined.  
  • Using the student's graph from "Ice Cream in Winter" ask the student to identify the Line of Best Fit.  (This should be a positive slope)
  • Ask the student to identify two points on the y-axis and two points on the x-axis which are on the Line of Best Fit. If the student has difficutly with idientifying these points, practice until the student is confident.  Have the student record these points using the students media of choice
  • Review the formula for slope with the student (using the different verbiage). Formula for Slope  = y2 - y1/x2 - x2 or Slope = the change in y/the change in x or Slope = rise/run
  • Have the student enter the coordinates into the formula.   Have the student calculate the slope.  A calculator can be used.  
  • Explain to the student that the slope can be used to interpolate values along the Line of Best Fit.  This will be reviewed in another lesson.  

ice cream in winter collage

Adapted from lesson 


  • Formula for Slope  = y2 - y1/x2 - x2 or Slope = the change in y/the change in x or Slope = rise/run
  • This is an opportunity to review the students ability to navigate values on a graph.