>Assuming that every question in this 20-question test has only 1 right answer and you choose to answer each question randomly, what is the chance that you're so bad that you only get 4 questions right or less?

They probably mean for you to assume that 1) each question has 5 answer choices, and 2) you select one of them with equal probability. But given that this is question #2, assumption (1) is kind of a guess, and (2) should be explicitly stated... (the answer btw has to do with the binomial distribution - and you definitely need some heavy arithmetic, so are they testing your gut instinct?)