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?
~$\frac{1}{12}$~
~$\frac{1}{6}$~
~$\frac{1}{5}$~
~$\frac{1}{3}$~
~$\frac{1}{2}$~
四个球随便排,4!,但其实两个红球和两个白球是一样的,所以24里面是有重复排列的情况,4!/2!*2!,这是分母。
分子就是1种情况。
不知道这么想对不对。
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