Solution :
It is given that :
Number of students in a random sample majoring in communication or psychology at an university = 250
Total number of students majoring in psychology = 100
Number of students majoring in psychology those who are happy = 80
So number of students majoring in psychology those who are not happy = 20
Total number of students majoring in communication = 250 - 100 = 150
Number of students majoring in communication those who are happy = 115
So number of students majoring in psychology those who are not happy = 35
a). Probability of the students happy with their major choices are
= 0.78
b). Psychology major
= 0.4
c). Probability of the students who are happy with the communication as the choice of major = = 0.46
d). Students unhappy with their choice of major given that the student is psychology major = = 0.018