Final answer:
The demand factor for the four-unit apartment with a dryer in each unit is 1.
Step-by-step explanation:
The demand factor is the ratio of the maximum demand of a system to its connected load. In this case, each unit in the four-unit apartment has a dryer. To calculate the demand factor, we need to consider the maximum demand of the dryers and the total connected load. Let's say each dryer has a maximum demand of 5,000 watts. The total connected load would be 4 times the maximum demand, which is 20,000 watts. Therefore, the demand factor for these units is 1, because the maximum demand is equal to the connected load.