JEE Main & Advanced Mathematics Probability Question Bank Odds in favour and odds against Addition theorem on probability

  • question_answer
    If \[{{A}_{1}},\,{{A}_{2}},...{{A}_{n}}\] are any n events, then

    A)                 \[P\,({{A}_{1}}\cup {{A}_{2}}\cup ...\cup {{A}_{n}})=P\,({{A}_{1}})+P({{A}_{2}})+...+P\,({{A}_{n}})\]

    B)                 \[P\,({{A}_{1}}\cup {{A}_{2}}\cup ...\cup {{A}_{n}})>P\,({{A}_{1}})+P({{A}_{2}})+...+P\,({{A}_{n}})\]

    C)                 \[P\,({{A}_{1}}\cup {{A}_{2}}\cup ...\cup {{A}_{n}})\le P\,({{A}_{1}})+P({{A}_{2}})+...+P\,({{A}_{n}})\]

    D)                 None of these

    Correct Answer: C

    Solution :

                       For any two events \[A\] and \[B,\]we have                    \[P(A\cup B)=P(A)+P(B)-P(A\cap B)\]                    \[\therefore \,\,\,P(A\cup B)\le P(A)+P(B).\]                 Using principle of mathematical induction, it can be easily established that \[P\left( \underset{i=1}{\overset{n}{\mathop{\cup }}}\,{{A}_{i}} \right)\le \sum\limits_{i=1}^{n}{P({{A}_{i}}).}\]


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