Probability of an event for a continuous random vector of three coordinates












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Let $X=(X_1,X_2,X_3)$ be a continuous random vector of the joint pdf $$f(x_1,x_2,x_3)= 12x_2 ;mathrm f mathrm o mathrm r ; 0<x_3<x_2<x_1<1$$ and $0$ elsewhere.



I need to find the probability of event $B$ where $B={x_3leq1/3}$. I've been able to sketch the support and see that it's a sort of pyramidal shape, and know that I should be able to find the probability via a triple integral.



My instinct says to simply set it up like so:
$$int_0^{1/3}int_{x_3}^{x_1}int_{x_2}^{1}12x_2;dx_1dx_2dx_3$$



but this is clearly wrong since the answer will still be in terms of a variable. If anyone could help me understand where I've been going wrong it would be greatly appreciated!










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    0












    $begingroup$


    Let $X=(X_1,X_2,X_3)$ be a continuous random vector of the joint pdf $$f(x_1,x_2,x_3)= 12x_2 ;mathrm f mathrm o mathrm r ; 0<x_3<x_2<x_1<1$$ and $0$ elsewhere.



    I need to find the probability of event $B$ where $B={x_3leq1/3}$. I've been able to sketch the support and see that it's a sort of pyramidal shape, and know that I should be able to find the probability via a triple integral.



    My instinct says to simply set it up like so:
    $$int_0^{1/3}int_{x_3}^{x_1}int_{x_2}^{1}12x_2;dx_1dx_2dx_3$$



    but this is clearly wrong since the answer will still be in terms of a variable. If anyone could help me understand where I've been going wrong it would be greatly appreciated!










    share|cite|improve this question











    $endgroup$















      0












      0








      0





      $begingroup$


      Let $X=(X_1,X_2,X_3)$ be a continuous random vector of the joint pdf $$f(x_1,x_2,x_3)= 12x_2 ;mathrm f mathrm o mathrm r ; 0<x_3<x_2<x_1<1$$ and $0$ elsewhere.



      I need to find the probability of event $B$ where $B={x_3leq1/3}$. I've been able to sketch the support and see that it's a sort of pyramidal shape, and know that I should be able to find the probability via a triple integral.



      My instinct says to simply set it up like so:
      $$int_0^{1/3}int_{x_3}^{x_1}int_{x_2}^{1}12x_2;dx_1dx_2dx_3$$



      but this is clearly wrong since the answer will still be in terms of a variable. If anyone could help me understand where I've been going wrong it would be greatly appreciated!










      share|cite|improve this question











      $endgroup$




      Let $X=(X_1,X_2,X_3)$ be a continuous random vector of the joint pdf $$f(x_1,x_2,x_3)= 12x_2 ;mathrm f mathrm o mathrm r ; 0<x_3<x_2<x_1<1$$ and $0$ elsewhere.



      I need to find the probability of event $B$ where $B={x_3leq1/3}$. I've been able to sketch the support and see that it's a sort of pyramidal shape, and know that I should be able to find the probability via a triple integral.



      My instinct says to simply set it up like so:
      $$int_0^{1/3}int_{x_3}^{x_1}int_{x_2}^{1}12x_2;dx_1dx_2dx_3$$



      but this is clearly wrong since the answer will still be in terms of a variable. If anyone could help me understand where I've been going wrong it would be greatly appreciated!







      probability probability-distributions






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      edited Jan 20 at 21:03







      sk13

















      asked Jan 20 at 20:25









      sk13sk13

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          2 Answers
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          It is $int_0^{1/3} int_{x_3}^{1} int_{x_2}^{1} 12x_2 dx_1dx_2dx_3$. (The middle integral cannot involve $x_1$. The condition $x_2 <x_1$ is already taken care of in the limits for $x_1$).






          share|cite|improve this answer









          $endgroup$





















            0












            $begingroup$

            Change the last integral from ($x_2$ to 1) to ($x_1$ to 1). Does it make any sense?






            share|cite|improve this answer









            $endgroup$













            • $begingroup$
              Sorry, I'm not sure I understand. Why would the bounds of $x_1$ be ($x_1$,1)?
              $endgroup$
              – sk13
              Jan 20 at 22:49













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            2 Answers
            2






            active

            oldest

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            2 Answers
            2






            active

            oldest

            votes









            active

            oldest

            votes






            active

            oldest

            votes









            1












            $begingroup$

            It is $int_0^{1/3} int_{x_3}^{1} int_{x_2}^{1} 12x_2 dx_1dx_2dx_3$. (The middle integral cannot involve $x_1$. The condition $x_2 <x_1$ is already taken care of in the limits for $x_1$).






            share|cite|improve this answer









            $endgroup$


















              1












              $begingroup$

              It is $int_0^{1/3} int_{x_3}^{1} int_{x_2}^{1} 12x_2 dx_1dx_2dx_3$. (The middle integral cannot involve $x_1$. The condition $x_2 <x_1$ is already taken care of in the limits for $x_1$).






              share|cite|improve this answer









              $endgroup$
















                1












                1








                1





                $begingroup$

                It is $int_0^{1/3} int_{x_3}^{1} int_{x_2}^{1} 12x_2 dx_1dx_2dx_3$. (The middle integral cannot involve $x_1$. The condition $x_2 <x_1$ is already taken care of in the limits for $x_1$).






                share|cite|improve this answer









                $endgroup$



                It is $int_0^{1/3} int_{x_3}^{1} int_{x_2}^{1} 12x_2 dx_1dx_2dx_3$. (The middle integral cannot involve $x_1$. The condition $x_2 <x_1$ is already taken care of in the limits for $x_1$).







                share|cite|improve this answer












                share|cite|improve this answer



                share|cite|improve this answer










                answered Jan 20 at 23:58









                Kavi Rama MurthyKavi Rama Murthy

                64.7k42766




                64.7k42766























                    0












                    $begingroup$

                    Change the last integral from ($x_2$ to 1) to ($x_1$ to 1). Does it make any sense?






                    share|cite|improve this answer









                    $endgroup$













                    • $begingroup$
                      Sorry, I'm not sure I understand. Why would the bounds of $x_1$ be ($x_1$,1)?
                      $endgroup$
                      – sk13
                      Jan 20 at 22:49


















                    0












                    $begingroup$

                    Change the last integral from ($x_2$ to 1) to ($x_1$ to 1). Does it make any sense?






                    share|cite|improve this answer









                    $endgroup$













                    • $begingroup$
                      Sorry, I'm not sure I understand. Why would the bounds of $x_1$ be ($x_1$,1)?
                      $endgroup$
                      – sk13
                      Jan 20 at 22:49
















                    0












                    0








                    0





                    $begingroup$

                    Change the last integral from ($x_2$ to 1) to ($x_1$ to 1). Does it make any sense?






                    share|cite|improve this answer









                    $endgroup$



                    Change the last integral from ($x_2$ to 1) to ($x_1$ to 1). Does it make any sense?







                    share|cite|improve this answer












                    share|cite|improve this answer



                    share|cite|improve this answer










                    answered Jan 20 at 20:43









                    ShaqShaq

                    3049




                    3049












                    • $begingroup$
                      Sorry, I'm not sure I understand. Why would the bounds of $x_1$ be ($x_1$,1)?
                      $endgroup$
                      – sk13
                      Jan 20 at 22:49




















                    • $begingroup$
                      Sorry, I'm not sure I understand. Why would the bounds of $x_1$ be ($x_1$,1)?
                      $endgroup$
                      – sk13
                      Jan 20 at 22:49


















                    $begingroup$
                    Sorry, I'm not sure I understand. Why would the bounds of $x_1$ be ($x_1$,1)?
                    $endgroup$
                    – sk13
                    Jan 20 at 22:49






                    $begingroup$
                    Sorry, I'm not sure I understand. Why would the bounds of $x_1$ be ($x_1$,1)?
                    $endgroup$
                    – sk13
                    Jan 20 at 22:49




















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