Ira S. answered 04/23/15
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the total revenue = the number of people * the price per trip.
According to your information then, the number of people can be represented by 20 + x.
The price per trip goes down for each additional person, so it can be represented by 10 - .25x
So the total revenue = (20 + x)(10 - .25x) multiplied out, this becomes
TR = 200 + 5x - .25x2 which is a parabola opening downward.
If you know calculus, take the derivative, set = to zero and solve. If not, the turning point is on the axis of symmetry.
So the axis of symmetry is x=-b/2a or x=-5/(-.5) = 10
So 10 people lead to a maximum revenue of (plug it into your total revenue function) $225.
Hope this helps.