So first, you need to determine how many rooms will be used. We are told that there is a total of 100 rooms, but we are running at 50% capacity. So we will use 50 rooms for this calculation.
Next, we need to find how many rooms 1 housekeeper can clean in their 8 hour shift. We are told that it takes them 25 minutes per room. This means they can clean 2.4 rooms per hour. So, 2.4 X 8 hours = 19.2 per shift.
Then we would take the total number of rooms that need to be cleaned (50) and divide by how many rooms 1 housekeeper can clean (19.2) = 2.6 and since you can't have .6 of a person, you should round up to 3.