求助一道GWD数学题！！！！！

GMAT8006

A certain roller coaster has3 cars, and a passenger is equally likely to ride in any 1 of the 3 cars eachtime that passenger rides the roller coaster. If a certain passenger is to ride the roller coaster 3 times, what isthe 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

Answer:C

请问是怎么算出来的？？？

violante

http://www.beatthegmat.com/a-certain-roller-coaster-has-3-cars-t18368.html

wzhang1217

prob 1st time: 3/3 he can ride any of the three cars
prob 2nd time: 2/3 he can choose from the two cars he has not ride
prob 3rd time: 1/3 only one of the three cars left

answer= 3/3 * 2/3 * 1/3 = 2/9