Question

Use the Quadratic equation to determine the last day that cowboy hats will be sold.

cowboy hats = -0.4x^2 + 20x + 10

Please help me work through this.

Answer 1

assuming x is the number of days,

h(x) is the number of hats sold on day x,
h=0 means no hats sold that day, because all were sold, so that is the last day.

h(x) = 0 when x = [-20 +/- sqrt(400+16)]/-.8
x = 50.5

so, some time during the 51st day sales went to zero.