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probability

by abhilashsiyer » Thu Nov 01, 2012 9:07 am
Probability of A attending class is 1/6 ,probability of B attending class is 1/5 . What is the probability that either A alone or B alone attends class?
1/10
1/5
3/10
1/3
11/30
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by pemdas » Thu Nov 01, 2012 10:34 am
abhilashsiyer wrote:Probability of A attending class is 1/6 ,probability of B attending class is 1/5 . What is the probability that either A alone or B alone attends class?
1/10
1/5
3/10
1/3
11/30
Since p(A)+p(B)>1 we infer the events A and B are not mutually exclusive, i.e. there's possibility that p(A&B)=p(A)*p(B) is there.

Thus, p(A)+p(B)-p(A)*p(B)=p(A or B), 1/6 + 1/5 - 1/30 = (5+6-1)/30 = 10/30 = 1/3
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