[Solved] A man lives on the tenth floor of a building. Every day he takes the elevator to go down to the ground floor to go to work. When he returns he takes the same elevator to the seventh floor and walks up the stairs to reach his apartment on the tenth floor. If there is someone else in the elevator with him or if it was raining that day, he goes back to the tenth floor directly. Note that there is nothing wrong with the elevator or the design of the building. It’s a perfectly normal elevator in a perfectly normal building. He hates walking up the stairs, so why does he do it?