求助一道概率题

meckychen

A gardener is going to plant 2 red rosebushes and 2 white rosebushes.  If the gardener is to select each of the bushes at random, one at a time, and plant them in a row, what is the probability that the 2 rosebushes in the middle of the row will be the red rosebushes?



A.      1/12

B.      1/6

C.      1/5

D.     1/3

E.      1/2

Answer: B可我不知道怎么算不来的？

yukizhang

一共可能的种法是4的全排列24（4＊3＊2＊1），两边黄中间红的种法，只能先从黄的2棵里挑1个，再从红的2棵里面挑1个，这样就是4（2＊2）种可能，剩下1红1黄没得组合，就只能先种红后种黄了。所以概率是4／24

dzh0619ABC

(A22*A22)/A44

huiguo85

红红白白，白白红红，红白红白，白红白红，白红红白，红白白红

sue101

1/2*2/3*1/2=1/6

lovesasa0820

顶3楼了