填空题 .A certain college has 8,978 full-time students, some of whom live on campus and some of whom live off campus.
    The following table shows the distribution of the 8,978 full-time students, by class and living arrangement.

									Freshmen						Sophomores							Juniors					Seniors
Live on campus									1,812						1,236							950					542
Live off campus									625						908							1,282					1,623

填空题 21.  If one full-time student is selected at random, what is the probability that the student who is chosen will not be a freshman?

填空题 22.  If one full-time student who lives off campus is selected at random, what is the probability that the student will be a senior?

填空题 23.  If one full-time student who is a freshman or sophomore is selected at random, what is the probability that the student will be a student who lives on campus?