<PRE><B>Question 185924</B>
the fuel efficiency of an average car is given by y= -0.0177x*2 + 1.48x + 3.39 where x is the speed im miles per hour and y is the fuel economy in miles per gallon.
1. find the speed at which an average car will get 20 mi/gal
solve  -0.0177x*2 + 1.48x + 3.39 = 20
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If that equation is really a quadratic there are two solutions:
x = 70.26 mph and x = 13.36 mph
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2. what speed yields the best fuel economy?
x = -b/2a = -1.48/(2*-0.0177) = 41.81 mph
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3. determine the range of speeds that yield 32 mi/gal or better
33.34 &lt;= x &lt;=  53.28 
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Cheers,
Stan H.
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