Final answer:
William and Mary should purchase 2 mixing machines for their Dairy Queen.
Step-by-step explanation:
To determine how many mixing machines William and Mary should purchase for their Dairy Queen, we need to calculate the maximum number of ice cream cones that can be produced in 8 hours of operation with a 50% capacity cushion.
Each mixing machine can produce 2 ice cream cones per minute, or 120 cones per hour. Thus, in 8 hours, one machine can produce 960 cones.
With a 50% capacity cushion, the maximum number of cones that can be produced is 960 x 1.5 = 1,440 cones.
Since they expect to sell an average of 2,000 cones in 8 hours, they need to purchase at least 2 machines (2 machines x 960 cones = 1,920 cones) to meet the expected demand. Therefore, William and Mary should purchase 2 mixing machines.