JEE Main & Advanced Mathematics Probability Question Bank Definition of probability

  • question_answer
    A box contains 3 white and 2 red balls. A ball is drawn and another ball is drawn without replacing first ball, then the probability of second ball to be red is      [Roorkee 1995]

    A)                 \[\frac{8}{25}\]    

    B)                 \[\frac{2}{5}\]

    C)                 \[\frac{3}{5}\]       

    D)                 \[\frac{21}{25}\]

    Correct Answer: B

    Solution :

               The second ball can be red in two different ways            (i) First is white and second red \[P(A)=\frac{3}{5}\times \frac{2}{4}=\frac{6}{20}\]            (ii) First is red and second is also red            \[P(B)=\frac{2}{5}\times \frac{1}{4}=\frac{2}{20}\]                 Both are mutually exclusive events, hence required probability is \[\frac{6}{20}+\frac{2}{20}=\frac{8}{20}=\frac{2}{5}.\]


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