A sample of midterm grades for five students showed the following results: $72,65,82,90,76 .$ Which of the following statements are correct, and which should be challenged as being too generalized?
a. The average midterm grade for the sample of five students is 77 .
b. The average midterm grade for all students who took the exam is 77 .
c. An estimate of the average midterm grade for all students who took the exam is 77 .
d. More than half of the students who take this exam will score between 70 and 85 .
e. If five other students are included in the sample, their grades will be between 65 and 90.