Intersection and conditioned set











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I don't understand why if it's true that $P(Acap B|C)=P(A|C)cdot P(B|C)$ (formula, moreover, used in a number of exercises), in this case he writes:
enter image description here










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    Actually, I do not believe that $P(Acap B|C)=P(A|C)cdot P(B|C)$ was used in the calculation. It seems more to be something like $P(Acap B|C)=P(A|B)cdot P(B|C)$. This is not true in general, there has to be some assumption on $A,B,C$. What is true however is that $P(Acap B|C)=P(A|B cap C)cdot P(B|C)$.
    – Matthias Klupsch
    Nov 21 at 10:28










  • @MatthiasKlupsch Thanks for your answer. Well, you're welcome to watch the solution that i post below.
    – Marco Pittella
    Nov 21 at 10:33










  • @MatthiasKlupsch I'm sorry for my reponse comment, i don't speak english so well. In any case, the photo up here is referring to the following exercise. You have 5 coins and $p_i$ is the probability that the $i$ coin gives Head (T), where $p_1=0,p_2=0,25,p_3=0,5,p_4=0,75,p_5=1$. One coin is extrracted and launched. You obtain Head (T). If the same $i$ coin launched again, what is the probability to obtain another Head (T)?
    – Marco Pittella
    Nov 21 at 10:48

















up vote
0
down vote

favorite
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I don't understand why if it's true that $P(Acap B|C)=P(A|C)cdot P(B|C)$ (formula, moreover, used in a number of exercises), in this case he writes:
enter image description here










share|cite|improve this question


















  • 1




    Actually, I do not believe that $P(Acap B|C)=P(A|C)cdot P(B|C)$ was used in the calculation. It seems more to be something like $P(Acap B|C)=P(A|B)cdot P(B|C)$. This is not true in general, there has to be some assumption on $A,B,C$. What is true however is that $P(Acap B|C)=P(A|B cap C)cdot P(B|C)$.
    – Matthias Klupsch
    Nov 21 at 10:28










  • @MatthiasKlupsch Thanks for your answer. Well, you're welcome to watch the solution that i post below.
    – Marco Pittella
    Nov 21 at 10:33










  • @MatthiasKlupsch I'm sorry for my reponse comment, i don't speak english so well. In any case, the photo up here is referring to the following exercise. You have 5 coins and $p_i$ is the probability that the $i$ coin gives Head (T), where $p_1=0,p_2=0,25,p_3=0,5,p_4=0,75,p_5=1$. One coin is extrracted and launched. You obtain Head (T). If the same $i$ coin launched again, what is the probability to obtain another Head (T)?
    – Marco Pittella
    Nov 21 at 10:48















up vote
0
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I don't understand why if it's true that $P(Acap B|C)=P(A|C)cdot P(B|C)$ (formula, moreover, used in a number of exercises), in this case he writes:
enter image description here










share|cite|improve this question













I don't understand why if it's true that $P(Acap B|C)=P(A|C)cdot P(B|C)$ (formula, moreover, used in a number of exercises), in this case he writes:
enter image description here







probability statistics elementary-set-theory boolean-algebra






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asked Nov 21 at 10:19









Marco Pittella

977




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  • 1




    Actually, I do not believe that $P(Acap B|C)=P(A|C)cdot P(B|C)$ was used in the calculation. It seems more to be something like $P(Acap B|C)=P(A|B)cdot P(B|C)$. This is not true in general, there has to be some assumption on $A,B,C$. What is true however is that $P(Acap B|C)=P(A|B cap C)cdot P(B|C)$.
    – Matthias Klupsch
    Nov 21 at 10:28










  • @MatthiasKlupsch Thanks for your answer. Well, you're welcome to watch the solution that i post below.
    – Marco Pittella
    Nov 21 at 10:33










  • @MatthiasKlupsch I'm sorry for my reponse comment, i don't speak english so well. In any case, the photo up here is referring to the following exercise. You have 5 coins and $p_i$ is the probability that the $i$ coin gives Head (T), where $p_1=0,p_2=0,25,p_3=0,5,p_4=0,75,p_5=1$. One coin is extrracted and launched. You obtain Head (T). If the same $i$ coin launched again, what is the probability to obtain another Head (T)?
    – Marco Pittella
    Nov 21 at 10:48
















  • 1




    Actually, I do not believe that $P(Acap B|C)=P(A|C)cdot P(B|C)$ was used in the calculation. It seems more to be something like $P(Acap B|C)=P(A|B)cdot P(B|C)$. This is not true in general, there has to be some assumption on $A,B,C$. What is true however is that $P(Acap B|C)=P(A|B cap C)cdot P(B|C)$.
    – Matthias Klupsch
    Nov 21 at 10:28










  • @MatthiasKlupsch Thanks for your answer. Well, you're welcome to watch the solution that i post below.
    – Marco Pittella
    Nov 21 at 10:33










  • @MatthiasKlupsch I'm sorry for my reponse comment, i don't speak english so well. In any case, the photo up here is referring to the following exercise. You have 5 coins and $p_i$ is the probability that the $i$ coin gives Head (T), where $p_1=0,p_2=0,25,p_3=0,5,p_4=0,75,p_5=1$. One coin is extrracted and launched. You obtain Head (T). If the same $i$ coin launched again, what is the probability to obtain another Head (T)?
    – Marco Pittella
    Nov 21 at 10:48










1




1




Actually, I do not believe that $P(Acap B|C)=P(A|C)cdot P(B|C)$ was used in the calculation. It seems more to be something like $P(Acap B|C)=P(A|B)cdot P(B|C)$. This is not true in general, there has to be some assumption on $A,B,C$. What is true however is that $P(Acap B|C)=P(A|B cap C)cdot P(B|C)$.
– Matthias Klupsch
Nov 21 at 10:28




Actually, I do not believe that $P(Acap B|C)=P(A|C)cdot P(B|C)$ was used in the calculation. It seems more to be something like $P(Acap B|C)=P(A|B)cdot P(B|C)$. This is not true in general, there has to be some assumption on $A,B,C$. What is true however is that $P(Acap B|C)=P(A|B cap C)cdot P(B|C)$.
– Matthias Klupsch
Nov 21 at 10:28












@MatthiasKlupsch Thanks for your answer. Well, you're welcome to watch the solution that i post below.
– Marco Pittella
Nov 21 at 10:33




@MatthiasKlupsch Thanks for your answer. Well, you're welcome to watch the solution that i post below.
– Marco Pittella
Nov 21 at 10:33












@MatthiasKlupsch I'm sorry for my reponse comment, i don't speak english so well. In any case, the photo up here is referring to the following exercise. You have 5 coins and $p_i$ is the probability that the $i$ coin gives Head (T), where $p_1=0,p_2=0,25,p_3=0,5,p_4=0,75,p_5=1$. One coin is extrracted and launched. You obtain Head (T). If the same $i$ coin launched again, what is the probability to obtain another Head (T)?
– Marco Pittella
Nov 21 at 10:48






@MatthiasKlupsch I'm sorry for my reponse comment, i don't speak english so well. In any case, the photo up here is referring to the following exercise. You have 5 coins and $p_i$ is the probability that the $i$ coin gives Head (T), where $p_1=0,p_2=0,25,p_3=0,5,p_4=0,75,p_5=1$. One coin is extrracted and launched. You obtain Head (T). If the same $i$ coin launched again, what is the probability to obtain another Head (T)?
– Marco Pittella
Nov 21 at 10:48












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        answered Nov 21 at 10:34









        Marco Pittella

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