3.(1)设A,B,C是三个事件,且 P(A)=P(B)=P(C)=1/4, P(AB)=P(BC)=0, P(AC)=1/8, 求A,B,C至少有一个发生的概率.(2)已知 P(A)=1/2, P(B)=1/3, P(C)=1/5, P(AB)=1/10, P(AC)=1/15, P(BC)=1/20, P(ABC)=1/30, 求 A cup B, overline (AB), A cup B cup C, overline (AB)C, A overline (B)C, overline (AB) cup C 的概率.(3)已知 P(A)=1/2, (i)若A,B互不相容,求 P(Aoverline (B) ), (ii)若 P(AB)=1/8, 求 P(Aoverline (B) ).

(1) 由容斥原理，$P(A \cup B \cup C) = \frac{5}{8}$。
(2) ① $P(A \cup B) = \frac{11}{15}$，② $P(\overline{A}\overline{B}) = \frac{4}{15}$，③ $P(A \cup B \cup C) = \frac{17}{20}$，④ $P(\overline{A}\overline{B}C) = \frac{7}{60}$，⑤ $P(\overline{A}\overline{B}C) = \frac{7}{60}$（或 $P(\overline{A}B\overline{C}) = \frac{13}{60}$），⑥ $P(\overline{A}\overline{B} \cup C) = \frac{7}{20}$。
(3) ① $P(A\overline{B}) = \frac{1}{2}$，② $P(A\overline{B}) = \frac{3}{8}$。

答案：
(1) $\boxed{\frac{5}{8}}$
(2) $\boxed{\frac{11}{15}, \frac{4}{15}, \frac{17}{20}, \frac{7}{60}, \frac{7}{60}, \frac{7}{20}}$
(3) $\boxed{\frac{1}{2}, \frac{3}{8}}$