Conditional probability, In studying the causes of power failures, the following data have been gathered:












0












$begingroup$


In studying the causes of power failures, the following data have been gathered:
10% are due to a transformer damage, 75% are due to line damage, 5% involve both
problems. Based on these percentages, find the probability that a given power failure
involves:



a) line damage given that there is transformer damage



b) transformer damage given that there is line damage



c) transformer damage but not line damage



d) transformer damage given that there is no line damage



e) transformer damage or line damage.



Now, I am familiar with conditional probabilities ( to some degree at least ) and the first thing that came to my mind for point a) was Bayes



so



$ T $ - it involves transformer damage



$ L $ - it involves line damage



$ B $ - it involves both



$$ P(L/T)=frac{P(L)*P(T/L)}{P(T)} $$



but the problem is that I am stuck at $P(T/L)$ I have no idea from were to start and maybe this approach is not even the correct one so I would appreciate some help, maybe a hint on how to proceed...










share|cite|improve this question









$endgroup$












  • $begingroup$
    Hint: use the definition of conditional probability
    $endgroup$
    – Alex
    Feb 2 at 1:53










  • $begingroup$
    Yes but first I need a complete system of events, and I just can't think of one
    $endgroup$
    – The Virtuoso
    Feb 2 at 1:56










  • $begingroup$
    Never mind, I'm such a douche we only worked with bayes and complete systems of events in my class that's why I couldn't think of a way to solve it, but I guess my answer could be found on wikipedia...
    $endgroup$
    – The Virtuoso
    Feb 2 at 2:06
















0












$begingroup$


In studying the causes of power failures, the following data have been gathered:
10% are due to a transformer damage, 75% are due to line damage, 5% involve both
problems. Based on these percentages, find the probability that a given power failure
involves:



a) line damage given that there is transformer damage



b) transformer damage given that there is line damage



c) transformer damage but not line damage



d) transformer damage given that there is no line damage



e) transformer damage or line damage.



Now, I am familiar with conditional probabilities ( to some degree at least ) and the first thing that came to my mind for point a) was Bayes



so



$ T $ - it involves transformer damage



$ L $ - it involves line damage



$ B $ - it involves both



$$ P(L/T)=frac{P(L)*P(T/L)}{P(T)} $$



but the problem is that I am stuck at $P(T/L)$ I have no idea from were to start and maybe this approach is not even the correct one so I would appreciate some help, maybe a hint on how to proceed...










share|cite|improve this question









$endgroup$












  • $begingroup$
    Hint: use the definition of conditional probability
    $endgroup$
    – Alex
    Feb 2 at 1:53










  • $begingroup$
    Yes but first I need a complete system of events, and I just can't think of one
    $endgroup$
    – The Virtuoso
    Feb 2 at 1:56










  • $begingroup$
    Never mind, I'm such a douche we only worked with bayes and complete systems of events in my class that's why I couldn't think of a way to solve it, but I guess my answer could be found on wikipedia...
    $endgroup$
    – The Virtuoso
    Feb 2 at 2:06














0












0








0


0



$begingroup$


In studying the causes of power failures, the following data have been gathered:
10% are due to a transformer damage, 75% are due to line damage, 5% involve both
problems. Based on these percentages, find the probability that a given power failure
involves:



a) line damage given that there is transformer damage



b) transformer damage given that there is line damage



c) transformer damage but not line damage



d) transformer damage given that there is no line damage



e) transformer damage or line damage.



Now, I am familiar with conditional probabilities ( to some degree at least ) and the first thing that came to my mind for point a) was Bayes



so



$ T $ - it involves transformer damage



$ L $ - it involves line damage



$ B $ - it involves both



$$ P(L/T)=frac{P(L)*P(T/L)}{P(T)} $$



but the problem is that I am stuck at $P(T/L)$ I have no idea from were to start and maybe this approach is not even the correct one so I would appreciate some help, maybe a hint on how to proceed...










share|cite|improve this question









$endgroup$




In studying the causes of power failures, the following data have been gathered:
10% are due to a transformer damage, 75% are due to line damage, 5% involve both
problems. Based on these percentages, find the probability that a given power failure
involves:



a) line damage given that there is transformer damage



b) transformer damage given that there is line damage



c) transformer damage but not line damage



d) transformer damage given that there is no line damage



e) transformer damage or line damage.



Now, I am familiar with conditional probabilities ( to some degree at least ) and the first thing that came to my mind for point a) was Bayes



so



$ T $ - it involves transformer damage



$ L $ - it involves line damage



$ B $ - it involves both



$$ P(L/T)=frac{P(L)*P(T/L)}{P(T)} $$



but the problem is that I am stuck at $P(T/L)$ I have no idea from were to start and maybe this approach is not even the correct one so I would appreciate some help, maybe a hint on how to proceed...







probability conditional-probability






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share|cite|improve this question











share|cite|improve this question




share|cite|improve this question










asked Feb 2 at 1:35









The VirtuosoThe Virtuoso

448




448












  • $begingroup$
    Hint: use the definition of conditional probability
    $endgroup$
    – Alex
    Feb 2 at 1:53










  • $begingroup$
    Yes but first I need a complete system of events, and I just can't think of one
    $endgroup$
    – The Virtuoso
    Feb 2 at 1:56










  • $begingroup$
    Never mind, I'm such a douche we only worked with bayes and complete systems of events in my class that's why I couldn't think of a way to solve it, but I guess my answer could be found on wikipedia...
    $endgroup$
    – The Virtuoso
    Feb 2 at 2:06


















  • $begingroup$
    Hint: use the definition of conditional probability
    $endgroup$
    – Alex
    Feb 2 at 1:53










  • $begingroup$
    Yes but first I need a complete system of events, and I just can't think of one
    $endgroup$
    – The Virtuoso
    Feb 2 at 1:56










  • $begingroup$
    Never mind, I'm such a douche we only worked with bayes and complete systems of events in my class that's why I couldn't think of a way to solve it, but I guess my answer could be found on wikipedia...
    $endgroup$
    – The Virtuoso
    Feb 2 at 2:06
















$begingroup$
Hint: use the definition of conditional probability
$endgroup$
– Alex
Feb 2 at 1:53




$begingroup$
Hint: use the definition of conditional probability
$endgroup$
– Alex
Feb 2 at 1:53












$begingroup$
Yes but first I need a complete system of events, and I just can't think of one
$endgroup$
– The Virtuoso
Feb 2 at 1:56




$begingroup$
Yes but first I need a complete system of events, and I just can't think of one
$endgroup$
– The Virtuoso
Feb 2 at 1:56












$begingroup$
Never mind, I'm such a douche we only worked with bayes and complete systems of events in my class that's why I couldn't think of a way to solve it, but I guess my answer could be found on wikipedia...
$endgroup$
– The Virtuoso
Feb 2 at 2:06




$begingroup$
Never mind, I'm such a douche we only worked with bayes and complete systems of events in my class that's why I couldn't think of a way to solve it, but I guess my answer could be found on wikipedia...
$endgroup$
– The Virtuoso
Feb 2 at 2:06










2 Answers
2






active

oldest

votes


















1












$begingroup$

According to your notation, we have $textbf{P}(T) = 0.1$, $textbf{P}(L) = 0.75$ and $textbf{P}(Tcap L) = 0.05$. Therefore:



(a) The sought probability is given by $textbf{P}(L|T)$, which can be rewritten as
begin{align*}
textbf{P}(L|T) = frac{textbf{P}(Lcap T)}{textbf{P}(T)} = frac{0.05}{0.1} = 0.5
end{align*}



(b) Analogously, we have
begin{align*}
textbf{P}(T|L) = frac{textbf{P}(Tcap L)}{textbf{P}(L)} = frac{0.05}{0.75} = frac{1}{15}
end{align*}



(c) Here, the event in which we are interested in is described by $textbf{P}(Tcap L^{c})$:
begin{align*}
textbf{P}(Tcap L^{c}) = textbf{P}(T) - textbf{P}(Tcap L) = 0.1 - 0.05 = 0.05
end{align*}



(d) In this case, the target event is described by $textbf{P}(T|L^{c})$:
begin{align*}
textbf{P}(T|L^{c}) = frac{textbf{P}(Tcap L^{c})}{textbf{P}(L^{c})} = frac{textbf{P}(Tcap L^{c})}{1 - textbf{P}(L)} = frac{0.05}{1 - 0.75} = frac{0.05}{0.25} = 0.2
end{align*}



(e) Finally, the last event is given by
begin{align*}
textbf{P}(Tcup L) = textbf{P}(T) + textbf{P}(L) - textbf{P}(Tcap L) = 0.1 + 0.75 - 0.05 = 0.8
end{align*}



Hope this helps.






share|cite|improve this answer











$endgroup$













  • $begingroup$
    Thank you very much, in my class we only worked with Bayes and complete system of events that's why when someone just mentioned me to use the definition of conditional probability I searched on wikipedia to make sure that I'm not missing something obvious and I just realized that I was...
    $endgroup$
    – The Virtuoso
    Feb 2 at 2:04










  • $begingroup$
    If you think my answer deserves it, give it a up vote.
    $endgroup$
    – APC89
    Feb 2 at 2:52



















1












$begingroup$

Going off my hint: recall that for two events $X$ and $Y$ (with $P(Y) neq 0$) we have



$$
P(X|Y) = frac{P(X cap Y)}{P(Y)}
$$



So in your case, you want



$$
P(L|T) = frac{P(L cap T)}{P(T)}
$$



Note that the event $L cap T$ is exactly $B$. So



$$P(L|T) = frac{P(B)}{P(T)}$$






share|cite|improve this answer









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    2 Answers
    2






    active

    oldest

    votes








    2 Answers
    2






    active

    oldest

    votes









    active

    oldest

    votes






    active

    oldest

    votes









    1












    $begingroup$

    According to your notation, we have $textbf{P}(T) = 0.1$, $textbf{P}(L) = 0.75$ and $textbf{P}(Tcap L) = 0.05$. Therefore:



    (a) The sought probability is given by $textbf{P}(L|T)$, which can be rewritten as
    begin{align*}
    textbf{P}(L|T) = frac{textbf{P}(Lcap T)}{textbf{P}(T)} = frac{0.05}{0.1} = 0.5
    end{align*}



    (b) Analogously, we have
    begin{align*}
    textbf{P}(T|L) = frac{textbf{P}(Tcap L)}{textbf{P}(L)} = frac{0.05}{0.75} = frac{1}{15}
    end{align*}



    (c) Here, the event in which we are interested in is described by $textbf{P}(Tcap L^{c})$:
    begin{align*}
    textbf{P}(Tcap L^{c}) = textbf{P}(T) - textbf{P}(Tcap L) = 0.1 - 0.05 = 0.05
    end{align*}



    (d) In this case, the target event is described by $textbf{P}(T|L^{c})$:
    begin{align*}
    textbf{P}(T|L^{c}) = frac{textbf{P}(Tcap L^{c})}{textbf{P}(L^{c})} = frac{textbf{P}(Tcap L^{c})}{1 - textbf{P}(L)} = frac{0.05}{1 - 0.75} = frac{0.05}{0.25} = 0.2
    end{align*}



    (e) Finally, the last event is given by
    begin{align*}
    textbf{P}(Tcup L) = textbf{P}(T) + textbf{P}(L) - textbf{P}(Tcap L) = 0.1 + 0.75 - 0.05 = 0.8
    end{align*}



    Hope this helps.






    share|cite|improve this answer











    $endgroup$













    • $begingroup$
      Thank you very much, in my class we only worked with Bayes and complete system of events that's why when someone just mentioned me to use the definition of conditional probability I searched on wikipedia to make sure that I'm not missing something obvious and I just realized that I was...
      $endgroup$
      – The Virtuoso
      Feb 2 at 2:04










    • $begingroup$
      If you think my answer deserves it, give it a up vote.
      $endgroup$
      – APC89
      Feb 2 at 2:52
















    1












    $begingroup$

    According to your notation, we have $textbf{P}(T) = 0.1$, $textbf{P}(L) = 0.75$ and $textbf{P}(Tcap L) = 0.05$. Therefore:



    (a) The sought probability is given by $textbf{P}(L|T)$, which can be rewritten as
    begin{align*}
    textbf{P}(L|T) = frac{textbf{P}(Lcap T)}{textbf{P}(T)} = frac{0.05}{0.1} = 0.5
    end{align*}



    (b) Analogously, we have
    begin{align*}
    textbf{P}(T|L) = frac{textbf{P}(Tcap L)}{textbf{P}(L)} = frac{0.05}{0.75} = frac{1}{15}
    end{align*}



    (c) Here, the event in which we are interested in is described by $textbf{P}(Tcap L^{c})$:
    begin{align*}
    textbf{P}(Tcap L^{c}) = textbf{P}(T) - textbf{P}(Tcap L) = 0.1 - 0.05 = 0.05
    end{align*}



    (d) In this case, the target event is described by $textbf{P}(T|L^{c})$:
    begin{align*}
    textbf{P}(T|L^{c}) = frac{textbf{P}(Tcap L^{c})}{textbf{P}(L^{c})} = frac{textbf{P}(Tcap L^{c})}{1 - textbf{P}(L)} = frac{0.05}{1 - 0.75} = frac{0.05}{0.25} = 0.2
    end{align*}



    (e) Finally, the last event is given by
    begin{align*}
    textbf{P}(Tcup L) = textbf{P}(T) + textbf{P}(L) - textbf{P}(Tcap L) = 0.1 + 0.75 - 0.05 = 0.8
    end{align*}



    Hope this helps.






    share|cite|improve this answer











    $endgroup$













    • $begingroup$
      Thank you very much, in my class we only worked with Bayes and complete system of events that's why when someone just mentioned me to use the definition of conditional probability I searched on wikipedia to make sure that I'm not missing something obvious and I just realized that I was...
      $endgroup$
      – The Virtuoso
      Feb 2 at 2:04










    • $begingroup$
      If you think my answer deserves it, give it a up vote.
      $endgroup$
      – APC89
      Feb 2 at 2:52














    1












    1








    1





    $begingroup$

    According to your notation, we have $textbf{P}(T) = 0.1$, $textbf{P}(L) = 0.75$ and $textbf{P}(Tcap L) = 0.05$. Therefore:



    (a) The sought probability is given by $textbf{P}(L|T)$, which can be rewritten as
    begin{align*}
    textbf{P}(L|T) = frac{textbf{P}(Lcap T)}{textbf{P}(T)} = frac{0.05}{0.1} = 0.5
    end{align*}



    (b) Analogously, we have
    begin{align*}
    textbf{P}(T|L) = frac{textbf{P}(Tcap L)}{textbf{P}(L)} = frac{0.05}{0.75} = frac{1}{15}
    end{align*}



    (c) Here, the event in which we are interested in is described by $textbf{P}(Tcap L^{c})$:
    begin{align*}
    textbf{P}(Tcap L^{c}) = textbf{P}(T) - textbf{P}(Tcap L) = 0.1 - 0.05 = 0.05
    end{align*}



    (d) In this case, the target event is described by $textbf{P}(T|L^{c})$:
    begin{align*}
    textbf{P}(T|L^{c}) = frac{textbf{P}(Tcap L^{c})}{textbf{P}(L^{c})} = frac{textbf{P}(Tcap L^{c})}{1 - textbf{P}(L)} = frac{0.05}{1 - 0.75} = frac{0.05}{0.25} = 0.2
    end{align*}



    (e) Finally, the last event is given by
    begin{align*}
    textbf{P}(Tcup L) = textbf{P}(T) + textbf{P}(L) - textbf{P}(Tcap L) = 0.1 + 0.75 - 0.05 = 0.8
    end{align*}



    Hope this helps.






    share|cite|improve this answer











    $endgroup$



    According to your notation, we have $textbf{P}(T) = 0.1$, $textbf{P}(L) = 0.75$ and $textbf{P}(Tcap L) = 0.05$. Therefore:



    (a) The sought probability is given by $textbf{P}(L|T)$, which can be rewritten as
    begin{align*}
    textbf{P}(L|T) = frac{textbf{P}(Lcap T)}{textbf{P}(T)} = frac{0.05}{0.1} = 0.5
    end{align*}



    (b) Analogously, we have
    begin{align*}
    textbf{P}(T|L) = frac{textbf{P}(Tcap L)}{textbf{P}(L)} = frac{0.05}{0.75} = frac{1}{15}
    end{align*}



    (c) Here, the event in which we are interested in is described by $textbf{P}(Tcap L^{c})$:
    begin{align*}
    textbf{P}(Tcap L^{c}) = textbf{P}(T) - textbf{P}(Tcap L) = 0.1 - 0.05 = 0.05
    end{align*}



    (d) In this case, the target event is described by $textbf{P}(T|L^{c})$:
    begin{align*}
    textbf{P}(T|L^{c}) = frac{textbf{P}(Tcap L^{c})}{textbf{P}(L^{c})} = frac{textbf{P}(Tcap L^{c})}{1 - textbf{P}(L)} = frac{0.05}{1 - 0.75} = frac{0.05}{0.25} = 0.2
    end{align*}



    (e) Finally, the last event is given by
    begin{align*}
    textbf{P}(Tcup L) = textbf{P}(T) + textbf{P}(L) - textbf{P}(Tcap L) = 0.1 + 0.75 - 0.05 = 0.8
    end{align*}



    Hope this helps.







    share|cite|improve this answer














    share|cite|improve this answer



    share|cite|improve this answer








    edited Feb 2 at 2:55

























    answered Feb 2 at 1:59









    APC89APC89

    2,371720




    2,371720












    • $begingroup$
      Thank you very much, in my class we only worked with Bayes and complete system of events that's why when someone just mentioned me to use the definition of conditional probability I searched on wikipedia to make sure that I'm not missing something obvious and I just realized that I was...
      $endgroup$
      – The Virtuoso
      Feb 2 at 2:04










    • $begingroup$
      If you think my answer deserves it, give it a up vote.
      $endgroup$
      – APC89
      Feb 2 at 2:52


















    • $begingroup$
      Thank you very much, in my class we only worked with Bayes and complete system of events that's why when someone just mentioned me to use the definition of conditional probability I searched on wikipedia to make sure that I'm not missing something obvious and I just realized that I was...
      $endgroup$
      – The Virtuoso
      Feb 2 at 2:04










    • $begingroup$
      If you think my answer deserves it, give it a up vote.
      $endgroup$
      – APC89
      Feb 2 at 2:52
















    $begingroup$
    Thank you very much, in my class we only worked with Bayes and complete system of events that's why when someone just mentioned me to use the definition of conditional probability I searched on wikipedia to make sure that I'm not missing something obvious and I just realized that I was...
    $endgroup$
    – The Virtuoso
    Feb 2 at 2:04




    $begingroup$
    Thank you very much, in my class we only worked with Bayes and complete system of events that's why when someone just mentioned me to use the definition of conditional probability I searched on wikipedia to make sure that I'm not missing something obvious and I just realized that I was...
    $endgroup$
    – The Virtuoso
    Feb 2 at 2:04












    $begingroup$
    If you think my answer deserves it, give it a up vote.
    $endgroup$
    – APC89
    Feb 2 at 2:52




    $begingroup$
    If you think my answer deserves it, give it a up vote.
    $endgroup$
    – APC89
    Feb 2 at 2:52











    1












    $begingroup$

    Going off my hint: recall that for two events $X$ and $Y$ (with $P(Y) neq 0$) we have



    $$
    P(X|Y) = frac{P(X cap Y)}{P(Y)}
    $$



    So in your case, you want



    $$
    P(L|T) = frac{P(L cap T)}{P(T)}
    $$



    Note that the event $L cap T$ is exactly $B$. So



    $$P(L|T) = frac{P(B)}{P(T)}$$






    share|cite|improve this answer









    $endgroup$


















      1












      $begingroup$

      Going off my hint: recall that for two events $X$ and $Y$ (with $P(Y) neq 0$) we have



      $$
      P(X|Y) = frac{P(X cap Y)}{P(Y)}
      $$



      So in your case, you want



      $$
      P(L|T) = frac{P(L cap T)}{P(T)}
      $$



      Note that the event $L cap T$ is exactly $B$. So



      $$P(L|T) = frac{P(B)}{P(T)}$$






      share|cite|improve this answer









      $endgroup$
















        1












        1








        1





        $begingroup$

        Going off my hint: recall that for two events $X$ and $Y$ (with $P(Y) neq 0$) we have



        $$
        P(X|Y) = frac{P(X cap Y)}{P(Y)}
        $$



        So in your case, you want



        $$
        P(L|T) = frac{P(L cap T)}{P(T)}
        $$



        Note that the event $L cap T$ is exactly $B$. So



        $$P(L|T) = frac{P(B)}{P(T)}$$






        share|cite|improve this answer









        $endgroup$



        Going off my hint: recall that for two events $X$ and $Y$ (with $P(Y) neq 0$) we have



        $$
        P(X|Y) = frac{P(X cap Y)}{P(Y)}
        $$



        So in your case, you want



        $$
        P(L|T) = frac{P(L cap T)}{P(T)}
        $$



        Note that the event $L cap T$ is exactly $B$. So



        $$P(L|T) = frac{P(B)}{P(T)}$$







        share|cite|improve this answer












        share|cite|improve this answer



        share|cite|improve this answer










        answered Feb 2 at 1:59









        AlexAlex

        52538




        52538






























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