I wish I would have read this article before I was asked some difficult questions in interviews. Here is a list of questions I have been asked (keep in mind, these were Skype interviews, no calculators allowed... but getting the right answer isn't the point):
How many weeks are in 12! seconds?
Given the population of England, is it possible for two people to have the same numbers of hairs on their head?
How many gas stations are in the U.S.?