8、the five letters DIGIT, two Is should be seperated by at least one other letter
答案C(4,2)*p(3,3)=36
9、DS:
Ten numbers 4 6 8 10 12 14 16 18 20 22, get rid of two, ask about the standard diviation
1) The mean is the same as that of the original set
2) 22 is not in the new set
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