Explain simply why 90 is the correct answer to: Hans booked a room in a hotel. The hotel has 10 floors with 10 identical rooms on each floor. Because of an accident, the last floor is unavailable for the guests. Considering there are no other guests, in how many different rooms could Hans be checked in?. Explanation:
The hotel has in total 10 floors * 10 rooms / floor = 100 rooms. One floor is unavailable, so Hans could be checked into 100 rooms - 10 rooms = 90 available rooms.