Question 130299
The peak corresponds to the vertex of the parabola. So let's find the x-coordinate of the vertex



In order to do that,  we can use this formula:


{{{x=-b/(2a)}}}


From the equation {{{y=-0.2x^2+12x+11.}}} we can see that a=-0.2 and b=12


{{{x=(-12)/(2*(-0.2))}}} Plug in b=12 and a=-0.2



{{{x=(-12)/(-0.4)}}} Multiply 2 and -0.2 to get -0.4



{{{x=30}}} Divide



So the x-coordinate of the vertex is  {{{x=30}}}





So at the x-coordinate of the vertex, the peak will occur. So on the 30th day, the peak in ticket sales will occur.