A website reports that 70% of its users are from outside a certain country, and 60% of its users logon the website every day. Suppose that for its users from inside the country, that 80% of them log onevery day. What is the probability that a person is from the country given that he logs on the websiteevery day? Has the probability that he is from the country increased or decreased with the additionalinformation?

Respuesta :

Answer:

The value is [tex]P (I | L ) = 0.63[/tex]

The probability has increased

Step-by-step explanation:

From the question we are told that

   The percentage that are from outside the country is  [tex]P(O) = 0.70[/tex]

    The  percentage that logs on everyday is  [tex]P(L) = 0.60[/tex]

    The  percentage that logs on everyday that are from the inside the country is     [tex]P(L | I) = 0.80[/tex]

Generally using Bayes' Rule the probability that a person is from the country given that he logs on the website every day is mathematically represented as

     [tex]P (I | L ) = \frac{P(I)* P(L|I)}{ P(O) *P(L|O) + P(I) *P(L|I) }[/tex]

Where  [tex]P(I)[/tex] is the percentage that are from inside that country which is mathematically represented as

       [tex]P(I) = 1 - P(O)[/tex]

      [tex]P(I) = 1 - 0.70[/tex]

      [tex]P(I) = 0.30[/tex]

And [tex]P(L| O)[/tex] is  percentage that logs on everyday that are from the outside  the country which is evaluated as

      [tex]P(L| O) = 1- P(L| I)[/tex]

       [tex]P(L| O) = 1- 0.80[/tex]

       [tex]P(L| O) = 0.20[/tex]

[tex]P (I | L ) = \frac{ 0.3* 0.80 }{ 0.7 *0.20 + 0.3 * 0.8 }[/tex]    

[tex]P (I | L ) = 0.63[/tex]

Given that the percentage that are from inside that country is  [tex]P(I) = 0.30[/tex]

and that the probability that a person is from the country given that he logs on the website every day is  [tex]P (I | L ) = 0.63[/tex]

We see that the additional information increased the probability

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