GWD1-9

meckychen · 发表于 2009-12-28 13:30:23

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 The answer is B , How to calculate?

meckychen · 发表于 2009-12-28 16:23:29

Anderuth · 发表于 2009-12-28 16:50:26

这样计算，4朵花排成一排的组合有2×（1＋2）＝6种情况，两朵红的在中间是一个组合，就得到六分之一了

GWD1-9

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