[問題] 請問一題數學
A dog breeder currently has 9 breeding dogs. 6 of the dogs have exactly 1
littermate, and 3 of the dogs have exactly 2 littermates. If 2 dogs are
selected at random, what is the probability that both selected dogs are NOT
littermates?
A. 1/6
B. 2/9
C. 5/6
D. 7/9
E. 8/9
想不出該怎麼組合才對呀! ="=
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