When I see that the 5th floor is on Friday, the first thing that comes to my mind is the 4th floor. Because consecutive numbers can't share a day, I know that it must be on Thursday.
_ _ _ _
_ 4 5 _ W T F S
Based on my 3 - 7 - 5 arrangement, I can add more to the diagram.
_ 7 _ _
3 4 5 _ W T F S
Notice that there is only one possible spot for 2. It cannot be on Monday because 3 is there, nor can it be on Saturday. It must be on Friday. This is why D is the correct answer. (Maybe our answer choices are mixed up. To be clear, the correct answer is "The second floor is examined on Friday.")
_ 7 2 _
3 4 5 8 W T F S
Because 2 must be on Friday, 8 must be on Saturday. 8 cannot be on Friday, which is why E is incorrect.
