JEE Main & Advanced Sample Paper JEE Main - Mock Test - 20

  • question_answer
    A and B toss a coin alternately on the understanding that the first to obtain heads wins the toss. The probability that A wins the toss

    A) \[\frac{1}{3}\]                        

    B)    \[\frac{2}{3}\]         

    C)   \[\frac{1}{4}\]                        

    D)    \[\frac{3}{4}\]

    Correct Answer: B

    Solution :

    Probability of getting the head by A in first chance \[=\frac{1}{2}\] Probability of losing the toss by A in first chance \[=1-\frac{1}{2}=\frac{1}{2}\] Probability of getting head by B in first chance \[=\left( \frac{1}{2} \right)\times \left( \frac{1}{2} \right)={{\left( \frac{1}{2} \right)}^{2}}\] Probability of getting head by A in second chance \[={{\left( \frac{1}{2} \right)}^{2}}\times \frac{1}{2}={{\left( \frac{1}{2} \right)}^{3}}\] ???????????.. ???????????.. The probability that A wins the toss. \[=\left( \frac{1}{2} \right)+{{\left( \frac{1}{2} \right)}^{3}}+{{\left( \frac{1}{2} \right)}^{5}}+....=\frac{1/2}{1-{{\left( \frac{1}{2} \right)}^{2}}}=\frac{2}{3}\]


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