帮看看这道概率题，谢谢

bobwangwbs

A certian roller coaster has 3 cars, and a passenger is equally likely to ride in any 1 of 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?

Answer is 2/9。 How?

strawdog

用1减去3次都坐同一个车的和2次坐同一个车的，过程确实比较复杂。

1-(1/3)^3-3*[(1/3)(1/3)(2/3)+(1/3)(2/3)(2/3)]=1-1/9-2/3=2/9

bobwangwbs

QUOTE:

P3/(3^3)=2/9

没有考虑到分子是全排列，我想，每个坐一次的话，只有一种坐法呢。原来应该考虑顺序！