China Naming Network - Ziwei knowledge - There are 6 players with 90 points, and the order of appearance is decided by lot. It is known that there are two qualified players in the 1 category, so find the probability that A is not in the first place and B is not in the last place according to the order of appearance.
There are 6 players with 90 points, and the order of appearance is decided by lot. It is known that there are two qualified players in the 1 category, so find the probability that A is not in the first place and B is not in the last place according to the order of appearance.
* * * There is a c (6,6) arrangement.
In the first * * *, A has C(5, 5) permutations.
B in the last * * *, there are C(5, 5) permutations.
A is in the first place, and B has a C (4 4,4) arrangement at the end.
The probability that A is not the first and B is not the last:1-c (5,5)+c (5,5)-c (4,4)/c (6,6) =1-30% = 70%.
Competition 1 the number of top three students in the class is x.
X =0, that is, Party A and Party B are in the last three places C (4,4 4) * C (3 3,2)/C (6,6) = 20%.
X = 1, that is, Party A and Party B are in the top three and one is in the bottom three. C (4，4) * C (3， 1) * C (3， 1) * 2/C (6，6) = 60%。
X =2, that is, C (4,4 4) * C (3 3,2)/C (6,6) = 20%.