Michael spends 1/2 an hour in every 1 room he cleans. This means that the number of 1/2 hour segments spent cleaning is equal to the number of rooms he cleans. If he cleaned for 3 hours, you can find the number of 1/2 hour segments within that time. One hour contains two 1/2-hour segments, since 1/2 hour + 1/2 hour = 1 hour. This means that 3 hours contains six 1/2 hour segments. Again, there is one 1/2 hour segment that corresponds to each room, so he cleaned a total of six rooms.
