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probability

by rickjan » Sun Nov 15, 2009 6:17 am
if the probability that event A will occur is 0.5 what's the probability that event B will occur?

1) the probability that both A and B will occur is 0.3
2) the probability that at least one of the events will occur is 0.8
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by life is a test » Sun Nov 15, 2009 6:31 pm
rickjan wrote:if the probability that event A will occur is 0.5 what's the probability that event B will occur?

1) the probability that both A and B will occur is 0.3
2) the probability that at least one of the events will occur is 0.8
IMO D

1. p(a) * p(b) = 0.3 -> 0.5 * p(b) = 0.3 -> suff
2. p(a) + p(b) + p(ab) = 0.8 = 0.5 + p(b) + 0.5*p(b) -> suff.
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by Stuart@KaplanGMAT » Sun Nov 15, 2009 7:55 pm
rickjan wrote:if the probability that event A will occur is 0.5 what's the probability that event B will occur?

1) the probability that both A and B will occur is 0.3
2) the probability that at least one of the events will occur is 0.8
Where's the question from? Did you copy it verbatim?

I'm sure that D is the intended answer to the question - but in order for either statement to be useful, we need to know that A and B are independent events.
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by 2010gmat » Fri Nov 20, 2009 6:57 am
Stuart when you say D is the intended answer...does it mean that its a trap or does it mean that D is the right answer
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by Stuart@KaplanGMAT » Fri Nov 20, 2009 7:52 am
2010gmat wrote:Stuart when you say D is the intended answer...does it mean that its a trap or does it mean that D is the right answer
It means that I think the question is worded very poorly; in its current form the answer should be E (not enough information), but my guess it that whoever wrote the question intended each statement to be sufficient alone.
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