The fuel efficiency (mpg rating) for cars has been increasing steadily since 1980. The formula for a car's average fuel efficiency for a given year between 1980 and 1996 is
E = 0.36. + 15.9
where E is miles per gallon and a is the number of years after 1980. Note: Round your answers down to get the
corresponding year. For instance, at = 3.89, the year is 1983.
a. In what years was the average fuel efficiency for cars less than 17 mpg (in interval form)?
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b. In what years was the average fuel efficiency for cars more than 20 mpg (in interval form)?
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Hint: The "start time" for this problem is 1980, not-o, and the "end time" is 1996 rather than o.