GWD10-Q02

[凱薩琳]

A certain roller coaster has 3 cars , and a passenger is equaly 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

Ans:C

請會的人幫忙解答阿 謝謝..

[sencerio]

坐三次，三次都要 把三台每一台坐過一次，也就是不能重覆坐任一台車

所以第一次坐的機率(3/3) <=三台隨便選一台坐都好
第二次坐的機率(2/3) <=第一次坐的那台已經不能再坐了
第三次坐的機率 (1/3) <=之前坐過的二台都不能再坐了

所以三次下來，把三台都坐過一次的機率就是
(3/3)x(2/3)x(1/3) = 6/27 = 2/9