A student takes a multiple-choice exam, in which each question has four items. Only one item presents the correct answer. Suppose she doesn't know the correct answer to any of the questions (she randomly selects the answer), she decided to use a strategy where she will put four balls (marked A, B, C, and D) inside a box. To answer each question, he randomly selects a ball and returns it to the box. The letter on the ball determines the item you select. Determine the probability of success. The exam is made up of nine questions.

• What is the probability that three questions are answered correctly?
• What is the probability that at least two are answered correctly?
• P(X7)=
• What is the probability that more than four are answered correctly?