If the hotel is charging the same rate for single and double occupancy, I would even argue that a single traveler should get something like $25 in this case since some hotel costs are based on the number of people: electricity, hot water, cold water, towel usage, facilities such as gyms and pools, wear and tear on the room, etc. Even housekeeping is more expensive for more people bacause they make more of a mess on average and may use more toiletries, especially in hotels with the big dispenser bottles of shampoo etc.