Question 1160819
Computer software programs are sold for $20 each. 
Three hundred people are willing to buy them at this price.
 For every $5 increase in price, there are 30 fewer people willing to buy the software.
 Calculate the selling price that will produce the maximum revenue.
:
let x = no. of 30 people groups subtracted
and
let x = no. $5 increases in price
:
Rev = price * units sold
R(x) = (20+5x)(300-30x)
FOIL
R(x) = 6000 - 600x + 1500x - 150x^2
A quadratic equation
y = -150x^2 + 900x + 6000
Max occurs on the axis of symmetry, x - -b/(2a)
x = {{{(-900)/(2*-150)}}}
x = +3 for max revenue
therefore
a 3(5) = $15 increase in price, 
20 + 15 = $35 is the price for max revenue
however
you lose 3(30) = 90 customers,  300 - 90 = 210 customers
:
"What is the maximum revenue?"
$35 * 210 = $7350