a calculus instructor uses computer-aided instruction and allows students to take the midterm exam as many times as needed until a passing grade is obtained. following is a record of the number of students in a class of 20 who took the test each number of times. studentsnumber of tests 101 72 23 14 a.use the relative frequency approach to construct a probability distribution. b.find the expected value of the number of tests taken. cpute the standard deviation.