A school's administrators are concerned about absenteeism at their school

Question

and the e�ect it has on students' grades. The following data were compiled, based on a sample of students.
Student's Absent Medium Absent
Grade Infrequently Absent Frequently
Low 1 9 8
Medium 6 35 7
High 8 9 2
a. What is the probability that a randomly selected student will have a low grade?

This would be 1/15 + 9/53 + 8/17 right?

b. What is the probability that a randomly selected student absent frequently?

8/18 + 7/48 + 2/19

c. Are grades and frequency in absent independent events? Why?

Not sure but i think they are dependent

d. Knowing that a randomly selected student has high grade, what is the probability that student is absent frequently?
2/19
e. What is the probability that a randomly selected student has either high grade or absent frequently?
I don't know how to calculate this

Answer 1

a. total of low grade students/grand total of students = 18/85

b. total of frequently absent students/grand total of students

c. Yes,try a Chi-squared (X^2) test to show why

d. Yes!

e. Either-or probabilities are found by adding the probabilities of the individual events. Total number of high grade/grand total + total number of absent frequently/grand total