Final answer:
To complete a project in 72 days instead of 90, the number of men required increases from 28 to 35, due to the inverse variation between the number of men and the time needed.
Step-by-step explanation:
The number of men needed to complete a project varies inversely with the time to complete the project. This means if the time decreases, the number of men needed will increase, and vice versa, according to the formula men × time = constant. If 28 men can complete the project in 90 days, we have:
28 men × 90 days = 2520 man-days (the constant).
To complete the project in 72 days, we can set up the equation:
men × 72 days = 2520 man-days.
Solving for the number of men (men = 2520 man-days / 72 days), we find that 35 men are required to complete the project in 72 days.