Please help me with this probability question...  TOPIC_SOLVED

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Please help me with this probability question...

Postby chaya.k.24 on Mon Jan 10, 2011 1:31 pm

QUESTION:To avoid detection at customs a traveler places 6 narcotics tablets in a bottle containg 9 vitamin pills that are similar in appearance.The the custom offical selects two of the tablets at random for analysis, what is the probability that the traveler will be arrested for illegal possesion of narcotics?

well i figured: probability of finding the drug in the first pill is 6/15 and the probability of find the drug in the next pill is 5/14.

Probability of finding the drug in at least one of the pills is 6/15 + 5/14 -(6/15 * 5/14) = 159/210 - 30/210 = 129/210=0.614 = 61.4%

????

Please let me know if i'm doing it wrong???
:)
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Postby stapel_eliz on Mon Jan 10, 2011 11:19 pm

Have you studied hypergeometric distributions yet? :wink:
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Re: Please help me with this probability question...

Postby chaya.k.24 on Tue Jan 11, 2011 8:09 am

@stapel_eliz: No... whats that? does that mean what i've done is wrong???
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Postby stapel_eliz on Tue Jan 11, 2011 12:11 pm

If they haven't covered the technique yet, then you're likely not expected to use it. But compare your answer with the ones provided in the links. :wink:
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Re: Please help me with this probability question...

Postby snowdrifter on Thu Jan 13, 2011 5:07 am

This one is easier to answer if you ask first what the probability of not getting caught is.
Find the probability that the first pill AND the second pill are vitamins.
One subtract that answer will tell you the probability of getting caught.
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