Posted by **Laura** on Sunday, October 12, 2008 at 6:27pm.

I am supposed to find the ticket sales of a concert using this formula:

N(x)= -0.3x^2 + 6x + 15

X represtents the number of days since the concert was first announced. I need to find out when daily ticket sales will peak and how many tickets will be sold on that day. How do i work out this problem I dont know the first place to start! please help.

- Algebra -
**bobpursley**, Sunday, October 12, 2008 at 6:41pm
If you are not in Calculus, then I would graph the equation to find x for the maximum sales.

- Algebra -
**Damon**, Sunday, October 12, 2008 at 6:49pm
I assume no calculus, therefore we must look at the shape of this curve.

it is of form ax^2 + bx + c, a parabola

y = -.3 x^2 + 6 x + 15

we need to find the vertex

complete the square

y/-.3 = x^2 +6/-.3 x +15/-.3

x^2 - 20x -50 = -3.33 y

x^2 -20 x = -3.33 y +50

x^2 -20 x +100 = -3.33y +150

(x-10)^2) = -3.33 ( y - 45)

vertex at (10,45)

10 days, 45 tickets

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