请教一道数学

A certain roller coaster has 3 cars, and a passenger is equally likely to ride in any 1 of the
3 cars each time that passenger rides the roller coaster. If a certain passenger is to ride
the roller coaster 3 times, what is the probability that the passenger will ride in each of
the 3 cars?
A. 0
B. 1/9
C. 2/9
D. 1/3
E. 1

答案是C.

我选B,请NN帮助提示解题思路.

是怎么判断用A(3,3)ＮＯＴ　Ｃ３，３呢

suppose the cars are marked sepertely as A, B, and C.

The first time, the guy will take any car. Set the car number is A.

The second time, he will have 3 choices: A, B and C. In order to take a different car. He has to chose B or C. The probablity is 2/3.

The third time, he still have 3 choces. However, he has only one choice -- the car he didn't take in the first and second time. The prabability is 1/3.

2/3*1/3=2/9

I very appreciate your thoughtfuldetailed explanation to my question.After reading your note, I get much better crossed thosed kind of questions.

Good luck with your application.

GPC 7109