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mathematics course [#permalink] New post 17 Oct 2010, 08:41
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John and Mary are taking a mathematics course. The course has only three
grades: A, B, and C. The probability that John gets a B is .3. The probability
that Mary gets a B is .4. The probability that neither gets an A but at least
one gets a B is .1. What is the probability that at least one gets a B but
neither gets a C?
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Re: mathematics course [#permalink] New post 23 Oct 2010, 19:31
abeer16 wrote:
John and Mary are taking a mathematics course. The course has only three
grades: A, B, and C. The probability that John gets a B is .3. The probability
that Mary gets a B is .4. The probability that neither gets an A but at least
one gets a B is .1. What is the probability that at least one gets a B but
neither gets a C?


Phew. Could not crack this question even after trying it for 10 minutes. Bunuel/Shrouded/Other GMATClub members -- Could you please help here?

Side note: How to bump up a thread??? Should someone just reply or is there a way to do it without replying to the post?
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Re: mathematics course [#permalink] New post 23 Oct 2010, 20:30
I am not convinced that this question is correct

P(neither a and at least one b) = P(both b) + P(one b, one c)

But, P(both b)=0.3*0.4=0.12>0.1

So this probability cannot be 0.1

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Re: mathematics course   [#permalink] 23 Oct 2010, 20:30
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