Question: Gasoline. Since clean-air regulations have dictated the use of unleaded gasoline, the supply of leaded gas in New York state has diminished. The table below was given on the August 2001 New York State Math B exam, a statewide achievement test for high school students.

Year                     1984        1988        1992        1996       2000

Gallons (1000's)       150          124          104          76          50

a) Create a linear model to predict the number of gallons that will be available in 2005.

b) The exam then asked students to estimate the year when leaded gasoline will first become unavailable, expecting them to use the model from part a to answer the question. Explain why that method is incorrect.

c) Create a model that would be appropriate for that task, and make the estimate. d) The "wrong" answer from the other model is fairly accurate in this case. Why?