Ah yes. thank you CB---seems I did not have the 3 at a time terms. So, I'm now using the following equation

__but I still don't receive the solution__ provide by the original person who stated the problem & solution:

P(A and B and C and D)=P(A)+P(B)+P(C)+P(D)

-P(A and B)-P(A and C)-P(A and D)-P(B and C)-P(B and D)-P(C and D)

+P(A and B and C)+P(A and B and D)+P(A and C and D)+P(B and C and D)

-P(A and B and C and D)

Question: Should the last term (A and B and C and D) be a minus or a plus?

Thanks for any comments