Answer:
- maximize P(x1, x2) = (x1)(38 -5x1) +(x2)(44 -5x2) +520 subject to 6x1 +8x2 ≤ 50
- (x1, x2) = (3, 4)
- P(3, 4) = 685
Step-by-step explanation:
Given
x1, x2 are units of production
6x1 +8x2 ≤ 50 . . . . limit on production hours
P = x1(38 -5x1) +x2(44 -5x2) +520 . . . . profit function
Find
a formulation for the optimization problem to maximize profit
the solution to that problem
maximum profit
Solution
There are a number of ways to approach this problem. One is to use the method of Lagrange multipliers. Another is to use the hour constraint to find x2 in terms of x1, then formulate the profit maximization as a problem in one variable. A graphical approach is another possibility.
For simplicity here, we'll try the second listed approach.
x2 = (50 -6x1)/8 = (25 -3x1)/4
Then the optimization problem is ...
maximize: P(x1) = x1(38 -5x1) +(25 -3x1)/4(44 -5/4(25 -3x1)) +520
for integer values of x1 and (25-3x1)/4
__
P(x) can be simplified to ...
P(x) = (-5/16)(25x^2 -166x -1919) = (-125/16)(x^2 -6.64x -76.76)
Converting this to vertex form, we have ...
P(x) = (-125/16)((x -3.32)^2 -65.7376)
The value of x1 that will optimize profit is x1 = 3.32. The corresponding value of x2 is (25-3×3.32)/4 = 3.76.
These are not integers, so we need to find integer values of x1 and x2 that satisfy the hour constraint and also maximize profit. We can start with ...
for (x1, x2) = (3, 4) . . . . hours needed are 6(3) +8(4) = 50 (OK)
profit is 3(38 -5×3) +4(44 -5×4) +520 = 685
__
We can verify this result using a graphical approach.
We find the profit function describes a circle with center (x1, x2) = (3.8, 4.4) and that maximizing profit is equivalent to finding the circle of smallest radius. Of course, the circle must pass through a grid point that is in the feasible region defined by the hours limit. The closest grid point to (3.8, 4.4) is (3, 4).