The cost of a first-class postage stamp changes over time. This change neither comes at precise intervals, nor does it increase a uniform amount over time. Students can use the change in price of a first-class postage stamp over time to practice modeling data in a linear function. Students should either locate, or be told, the price of stamps over a given period of time. Tell your students they must use at least ten data points. Have them plot the cost on the Y axis of a graph and the year on the X axis. Then, have the students calculate the X and Y intercepts, explain their significance, and calculate a line of best fit for the data.
The federal minimum wage is another number that varies inconsistently over time. It does not increase every year, and when it is raised, it is not increased by a uniform amount. Have your students research, or give them, the federal minimum wage for the past 50 years or so. Tell them to use at least ten data points. Then have your students plot the minimum wage on the Y axis and the year on the X axis. Then have them locate the X and Y intercepts, explain their significance, and plot a line of best fit for the data.
The number of students enrolled in the public college system of the state of New York is another good real-life example. The number is not controlled by a single entity, such as congress or the post office, so its increase or decrease will be good practice for modeling real-life trends. Have your students research this information, though it is more difficult to find, so you may wish to give it to them. Tell them to use at least ten data points. Have them plot the enrollment on the Y axis and the year on the X axis. Then have them calculate the X and Y intercepts, explain their meaning, and calculate a line of best fit. For this project, you may wish to truncate the number into only three digits and denote the units as being thousands. Thus, 449,547 would become 449. With such large numbers, the sacrifice of accuracy is small, and it will make the calculations less messy for your students.