Two thirds of eth students in a class are boys and the rest girls. It is known that eh probability of a girl getting a first class is 0.25 and that of

Monjur Alahi

Two thirds of eth students in a class are boys and the rest girls. It is known that eh probability of a girl getting a first class is 0.25 and that of a boy getting a first class is 0.28. find the probability that a student chosen at random will get first class marks in the subject.


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Salim Ahmed Kawsar

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Correct Answer - `0.27`
We have `P(G)=1//3and P(B)=2//3`
` P(A//G)=0.25and P(A//B)=0.28`
Here, A is the event that student chosen will get a first class.
So, using total probability theorem,
`P(A)=P(B)P(A//B)+P(G)P(A//G)`
`2/3xx0.28+1/3xx0.25=0.27`

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