Final answer:
Ned should allocate the additional 120 machine hours to produce hammers because they yield a higher total contribution margin of $36,000 compared to screwdrivers which would provide $33,600.
Step-by-step explanation:
To decide which product to allocate the additional 120 machine hours to, we should calculate the total additional contribution margin for each product. We have the contribution margin per unit of limited resource for hammers at $300 and screwdrivers at $280. We also have the unit contribution margin per product, being $150 for hammers and $170 for screwdrivers. While the unit contribution margin is higher for screwdrivers, what matters in this context is the contribution margin per unit of the limited resource, which represents the additional profit Ned would earn per machine hour if he produced that product.
The hammers would provide an additional contribution margin of 120 machine hours X $300 = $36,000. Meanwhile, the screwdrivers would provide an additional contribution margin of 120 machine hours X $280 = $33,600. Therefore, Ned should allocate the additional machine hours to produce hammers, as they yield a higher total contribution margin.