Using inclusion-exclusion, P(A∪B∪C)P(A \cup B \cup C)P(A∪B∪C) equals:
P(A)+P(B)+P(C)−P(A∩B)−P(A∩C)−P(B∩C)+P(A∩B∩C)P(A)+P(B)+P(C)-P(A\cap B)-P(A\cap C)-P(B\cap C)+P(A\cap B\cap C)P(A)+P(B)+P(C)−P(A∩B)−P(A∩C)−P(B∩C)+P(A∩B∩C)
P(A)+P(B)+P(C)P(A)+P(B)+P(C)P(A)+P(B)+P(C)
P(A)+P(B)+P(C)−P(A∩B∩C)P(A)+P(B)+P(C)-P(A\cap B\cap C)P(A)+P(B)+P(C)−P(A∩B∩C)
1−(P(Ac)+P(Bc)+P(Cc))1-(P(A^c)+P(B^c)+P(C^c))1−(P(Ac)+P(Bc)+P(Cc))