Sagot :
Answer:
a) In the interval of [1980,1983].
b) In the interval of [1991, 1996].
Step-by-step explanation:
Fuel efficiency:
The fuel efficiency, for the cars, in x years after 1980, is given by:
[tex]E(x) = 0.36x + 15.9[/tex]
15.9 is the fuel efficiency in 1980.
a. In what years was the average fuel efficiency for cars less than 17 mpg (in interval form)?
From 1980 to:
[tex]E(x) < 17[/tex]
[tex]0.36x + 15.9 < 17[/tex]
[tex]0.36x < 1.1[/tex]
[tex]x < \frac{1.1}{0.36}[/tex]
[tex]x < 3.06[/tex]
3.06 = 1980 + 3 = 1983. So
In the interval of [1980,1983].
b. In what years was the average fuel efficiency for cars more than 20 mpg (in interval form)?
From x until 1996.
[tex]E(x) > 20[/tex]
[tex]0.36x + 15.9 > 20[/tex]
[tex]0.36x > 4.1[/tex]
[tex]x > \frac{4.1}{0.36}[/tex]
[tex]x > 11.38[/tex]
11.38 = 1980 + 11 = 1991. So
In the interval of [1991, 1996].