<PRE><B>Question 80427</B>
The average number of diners in a restaurant can be modeled with the function 
D(t)= -2t^2+20t+15 , where t is the number of hours after 8:00 A.M. At what time is the number of diners at its maximum?

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You have a quadratic with a=-2 , b=20
Max occurs when t=-b/2a = -20/(2*-2)= 5 hurs
5hrs after 8:00AM is 1:PM
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Cheers,
Stan H.</PRE>