Question 178883
The equation is tickets= -0.2x^2+12x+11. 
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By inspecting the coefficient associated with the x^2 term, we see that it is negative therefore the parabola is opens downward.  If so, finding the vertex will tell us the maximum.
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axis of symmetry = -b/2a 
= -12/(2(-0.2))
= -12/(-0.4)
= 30 days (days would the peak occur)
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Setting the equation to zero then solve for x:
0 = -0.2x^2+12x+11
Since we can't factor, solve using the quadratic equation.  Doing so, yields:
x = {-0.9, 60.9}
Tossing out the negative solution the answer is:
61 days (number of days before tickets are sold)
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Details of quadratic:
*[invoke quadratic "x", -.2, 12, 11 ]