The membership of a committee consists of 3 English teachers, 4 Mathematics teachers, and 2 Social Studies teachers. If 2 committee members are to be selected at random to write the committee’s report, what is the probability that the two members selected will both be English teachers?
~$\frac{2}{3}$~
~$\frac{1}{3}$~
~$\frac{2}{9}$~
~$\frac{1}{12}$~
~$\frac{1}{24}$~
粗心
选择第一个et概率为:3/9, 选择第二个et的概率为:2/8, 所以,3/9 * 2/8 = 1/12
共 C92=36 种情况,2个都是English teachers = C32 = 3, 所以probability = 3/36=1/12