probability

[rickjan]

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

[life is a test]

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.

[Stuart@KaplanGMAT]

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.

[2010gmat]

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

[Stuart@KaplanGMAT]

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.