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An examination consists of two papers , paper1 and paper2 . the probability of failing in paper 1 is 0.3 and that in paper 2 is 0.2 . Given that a student has failed in paper2 , the probability of failing in paper1 is 0.6 .The probability of student failing in both papers is ...?

ans : 0.12 ...

now i simply got the ans by putting values in formula ... no problem , but i tried with other methed

i just creat sample space and then try to find probability, what's wrong here ? Someone verify pls ...M getting different ans ...

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@joshi_nitesh

Given that a student has failed in paper2 , the probability of failing in paper1 is 0.6.

First of all, it is a conditional probability.

and given that P(F1 ∣  F2) = 0.6  ,P(F1) =.3 ,P(F2) =.2

By conditional Probability

P(F1 ∩ F2) = P(F2) .P(F1 ∣  F2) = .2 * .6 =0.12

You can also solved this Qs by Other methods too but you need you to study Renormalization concept .Your soln is wrong due to this.

For Cp I recommend watch Harvard stat101 conditional probability lectures 4 and 5.

answered by Boss (8.8k points) 3 8 12

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