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Probability

Question
CBSEENMA12033726

Probabilities of solving a specific problem independently by A and B are 1 half space and space 1 third respectively. If both try to solve the problem independently, find the probability:
(i) the problem is solved    (ii) exactly one of them solves the problem.

Solution
(i) The probabilities of A and B solving the problem are 1 half space and space 1 third respectively. 
i.e.     straight P left parenthesis straight A right parenthesis space equals 1 half comma space space straight P left parenthesis straight B right parenthesis space equals space 1 third
therefore the probabilities of A and B solving the problems are 1 minus 1 half comma space space 1 minus 1 third.
i.e.,               1 half comma space 2 over 3 respectively.
therefore   probability that problem is not solved by A and B  = 1 half cross times 2 over 3 space equals space 1 third
therefore  probability that the problem is solved = 1 minus 1 third equals space space 2 over 3
(ii) P(exactly one of them solves the problem)
            equals space straight P left parenthesis straight A space straight B with bar on top space space or space space straight A with bar on top space straight B right parenthesis space equals space straight P left parenthesis straight A space straight B with bar on top right parenthesis space plus space left parenthesis straight A with bar on top space straight B right parenthesis
equals space straight P left parenthesis straight A right parenthesis thin space straight P left parenthesis straight B with bar on top right parenthesis space plus space straight P left parenthesis straight A with bar on top right parenthesis thin space straight P left parenthesis straight B right parenthesis
space equals space straight P left parenthesis straight A right parenthesis space left square bracket 1 space minus space straight P left parenthesis straight B right parenthesis right square bracket space plus space left square bracket 1 space minus space straight P left parenthesis straight A right parenthesis right square bracket space straight P left parenthesis straight B right parenthesis
space equals space open parentheses 1 half close parentheses space open square brackets 1 minus 1 third close square brackets space plus space open square brackets 1 minus 1 half close square brackets space open parentheses 1 third close parentheses
space equals space 1 half cross times 2 over 3 cross times 1 half cross times 1 third space equals space 1 third plus 1 over 6 space equals fraction numerator 2 plus 1 over denominator 6 end fraction space equals 3 over 6 space equals 1 half

space

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