P(A cup B cup C) = P(A) + P(B cup C) - P(A cap ((B cup C))) = P(A) + P(B) + P(C) - P(B cap C) - P(A cap ((B cup C))) Or P(A cap ((B cup C))) = P(((A cap B)) cup ((A cap C))) = P(A cap B) + P(A cap C) - P(((A cap B)) cap ((A cap C))) = P(A cap B) + P(A cap C) - P(A cap B cap C) Donc P(A cup B cup C) = P(A) + P(B) + P(C) - P(B cap C) - P(B cap A) - P(A cap C) + P(A cap B cap C)