Re: thank you
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Sorry, I misstated it in my answer. You need the second equation as well. The second and fourth together tell us that the probability of c U (not (a U b U d U e)) is 0.2 (since taking c out reduces the probability from 1 to 0.8). Therefore P(c U (not a)) >= 0.2. P(a U c) = P(a) + P(not a U c) = 0.4, so P(a) <= 0.2.
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I think you mean,
Sorry, I misstated it in my answer. You need the second equation as well. The second and fourth together tell us that the probability of c intersect (not (a U b U d U e)) is 0.2 (since taking c out reduces the probability from 1 to 0.8). Therefore P(c intersect (not a)) >= 0.2. P(a U c) = P(a) + P( (not a) intersect c) = 0.4, so P(a) <= 0.2.
PairTheBoard
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