Question 881806
the formula is:
p(a or b or c) = p(a) + p(b) + p(c) - p(ab) - p(ac) - p(bc) + p(abc).


p(ab) = p(a) * p(b).
p(ac) = p(a) * p(c).
p(bc) = p(b) * p(c).
p(abc) = p(a) * p(b) * p(c).


use that formula and you will find that the problem will be solved 3/4 of the time.