I used to work as an actuary, so I can give some input to the question asked earlier.
The questions asked on the actuarial exams are the highest level of difficulty. They spend days coming up with each question, trying to make it as difficult as possible. Not only that, they do research on the most common mistakes made while solving the questions, and offer them up as answers in the multiple choice questions.
I went into those exams thinking I knew the material really, really well, and walked out knowing I failed miserably.