Final Answer:
To maximize her profit at the craft show, Mrs. McGee should make 20 pins and 10 pairs of earrings.
Step-by-step explanation:
Define variables:
p: Number of pins
e: Number of pairs of earrings
t: Total time available (40 hours)
m: Minimum number of items (20)
pp: Profit per pin ($8)
pe: Profit per pair of earrings ($20)
Constraints:
Time constraint: p + 2e <= t => p + 2e <= 40
Minimum items constraint: p + e >= m => p + e >= 20
Variety constraint: p >= e
Objective function:
Maximize total profit: P(p, e) = pp * p + pe * e
Method:
Convert the constraints into inequalities:
Time: 2e <= 40 - p => e <= 20 - p/2
Minimum items: e >= 20 - p
Variety: p >= e
Substitute the time constraint into the objective function:
P(p) = pp * p + pe * (20 - p/2)
Differentiate P(p) and set it equal to zero to find the optimal p:
dP(p)/dp = pp - pe/2 = 0
Solving for p: p = 2e
Substitute p = 2e into the constraints:
e <= 20 - 2e/2 => e <= 10
e >= 20 - 2e => e >= 6.67
2e >= e => e <= 2e
The feasible range for e is 6.67 <= e <= 10.
We want to maximize P(p), so we choose the highest value of e within the feasible range: e = 10.
Calculate the corresponding number of pins: p = 2e = 20.
Results:
Number of pins (p): 20
Number of pairs of earrings (e): 10
Total profit: P(20, 10) = 8 * 20 + 20 * 10 = $360
Therefore, Mrs. McGee should make 20 pins and 10 pairs of earrings to maximize her profit at the craft show.