Question 435552
I will assume that both of them will pass the exam ONLY IF their answers are the same (in which case it will convince the professor that they really had a flat!).  Student 1 has 4 choices, and student 2 has also 4 choices.  Hence there are 4*4 = 16 ways for the 2 students to give their answers.  Of these, there are only 4 ways that both of them could give the same answer.  Thus the probability that the students pass is 4/16, or 1/4.