J & K CET Engineering J and K - CET Engineering Solved Paper-2015

  • question_answer
    A crime is committed by one of two suspects, A and B. Initially, there is equal evidence against both of them. In further investigation at the crime scene, it is found that the guilty party had a blood type found in 20% of the population. If the suspect A does match this blood type, whereas the blood type of suspect B is unknown, then the probability that A is the guilty party, is             

    A)  \[\frac{3}{5}\]

    B)  \[\frac{5}{6}\]

    C)  \[\frac{1}{3}\]

    D)  \[\frac{2}{3}\]

    Correct Answer: B

    Solution :

    Consider, the events \[{{E}_{1}},\,{{E}_{2}}\] and A \[P({{E}_{1}})=\frac{1}{2}.\,P({{E}_{2}})=\frac{1}{2}\] \[P({{E}_{1}}/A)=\frac{20\times 100}{100\times 100},\,\,P({{E}_{2}}/A)=\frac{20\times 20}{100\times 100}\] \[\therefore \]  Required probability \[P(A/{{E}_{1}})=\frac{P({{E}_{1}})\times P({{E}_{1}}/A)}{P({{E}_{1}})\times P({{E}_{1}}/A)+P({{E}_{2}})\times P({{E}_{2}}/A)}\] \[=\frac{\frac{1}{2}\times \frac{20\times 100}{100\times 100}}{\frac{1}{2}\times \frac{20\times 100}{100\times 100}+\frac{1}{2}\times \frac{20\times 20}{100\times 100}}\] \[=\frac{20\times 100}{20\times (100+20)}=\frac{100}{120}=\frac{5}{6}\]


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