There are 3 students, 2 students and 5 students in Grade Two 1 Class, Class Two and Class Three respectively. If the order of their speeches is decided by drawing lots, what is the probability that three people in Grade 2 1 Class are arranged together and two people in Class 2 are separated?
Total number of events = 10!
1 class three people line up together. Number of species =3! , as a whole
There are six people in class three, all in six rows! grow
There are two people in class 2, and the number of species =7*6.
So P=3! *6! *7*6/ 10! = 1/20