Question

In planning a restaurant, it is estimated that a profit of $8 per seat will be made if the number of seats is no more than 50 inclusive. On the other hand, the profit on each seat will decrease 10 cents for each seat above 50.

a) Find the number of seats that will produce the maximum profit.
b) What is the maximum profit?

Answer 1

a. 65 seats

b. $422.50

Explanation:

We have the following two functions:

8 * x, {0 <= x <= 50}

x * (8 - 0.1 * (x - 50)), {x> 50}, solving we have:

-0.1 * x ^ 2 + 13 * x, {x> 50}

Now we derive both functions and we are left with:

8, {0 <= x <= 50}

-0.2 * x + 13 {x> 50}

we cannot equal to 0 the first function that is equal to 0, because it would be inconsistent, therefore we equal the second function to 0:

-0.2 * x + 13 = 0

0.2 * x = - 13

x = -13 / -0.2

x = 65

Now, test for increasing and decreasing on the intervals (0.65) and (65, infinity)

p '(60) = -0.2 * (60) + 13 = 1

since this value is positive the profit is increasing on (0.65)

p '(70) = -0.2 * (70) + 13 = -1

becuase this value is negative the profit is decreasing on (65, infinity)

Therefore 65 seats are needed to maximize profit

The maximum value would be:

P (65) = 0.1 * (65 ^ 2) + 13 * 65 = 422.5

That is, the maximum value is $ 422.50