怎么样思考哦?

shayuamerica

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

Shirley8023

P(3,3)/3C(1,3)

shayuamerica

不是很理解!能详细点吗?我看概略都有点忘记了!

Shirley8023

3次坐3节不同的车厢，即：P(3,3)。3次随便坐这3节车厢的组合有：C(1,3)xC(1,3)xC(1,3)或者可以理解为每次C(1,3),3次即3C(1,3)。那么概率就是P(3,3)/3C(1,3)了。不好意思，解释得不好。你再理解一下看看。

newengland

简单一点，分3次坐

第一次：肯定会坐上其中一个 (假设是A)

第二次：2/3机会不会坐上第一次坐的那辆 ( B or C)

第三次：1/3机会坐上前两次没坐过的那辆 ( C if B was taken, or B if C was taken)

then 1*2/3*1/3 = 2/9

shayuamerica

理解了!谢谢帮助哦!