Help with letter b and c

13. A test consists of 20 multiple choice questions, each with five possible answers, only one of which is correct. a. Find the mean and the standard deviation of the number of correct answers, if a student was just guessing at random. b. Find the probability of a student getting exactly 7 correct, if the student was just guessing at random. You may use software, table, formula, or calculator, whatever, just show me how you got your answer. c. Would it be 'unusual' for a student to get 8 correct by simply guessing? Explain your