Compute $P{tlt Xlt Y}$ for $t ge 0$, when $X$ and $Y$ are independent exponential random variables, possibly...












0












$begingroup$



What is $P(t lt X lt Y)$ for $tgt 0$, when X and Y are independent exponential variables with the parameters $lambda$ and $mu$ respectively?




Since X and Y are independent, I got joint PDF to be $lambda cdotmucdot
e^{-lambdacdot x-mucdot y}$
.



Now that I'm looking for $P(t lt X lt Y)$, using the joint PDF, I set it as:
$$
P(t<X<Y)=int_0^inftyint_t^y lambda cdotmucdot
e^{-lambdacdot x-mucdot y}dxdy
$$



Is this correct? I'm trying to solve it using the online integral calculator but it's not getting the answer.





Edit 1: Here are the changes and result I came up with



Edit 2: Fixed my calculation error and got a confident answer:
$$
P(t<X<Y)=int_t^inftyint_t^y lambda cdotmucdot
e^{-lambdacdot x-mucdot y}dxdy=frac{lambda}{lambda+mu}e^{-t(lambda+mu)}
$$



I would really appreciate if someone could check if this is correct. Thank you!










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$endgroup$








  • 1




    $begingroup$
    Well, even without the help of online tools, you should be able to compute $$int_t^ylambda e^{-lambda x}dx$$ and to plug the result in the integral with respect to $x$...
    $endgroup$
    – Did
    Jan 11 at 16:11










  • $begingroup$
    Observe that $t < X < Y$ implies $t < Y$ and hence, the "domain of integration" (as Americans call it) is the set of $y$ such that $t < y.$ Having such a fix $y,$ the domain of integration of $X$ is simply $t < x < y.$ What I am expressing here is that your double integral is wrong.
    $endgroup$
    – Will M.
    Jan 11 at 16:51










  • $begingroup$
    @WillM. Since $t<y$, would the limit of the $dy$ integral be from t to $infty$?
    $endgroup$
    – hilageryolo
    Jan 11 at 20:03


















0












$begingroup$



What is $P(t lt X lt Y)$ for $tgt 0$, when X and Y are independent exponential variables with the parameters $lambda$ and $mu$ respectively?




Since X and Y are independent, I got joint PDF to be $lambda cdotmucdot
e^{-lambdacdot x-mucdot y}$
.



Now that I'm looking for $P(t lt X lt Y)$, using the joint PDF, I set it as:
$$
P(t<X<Y)=int_0^inftyint_t^y lambda cdotmucdot
e^{-lambdacdot x-mucdot y}dxdy
$$



Is this correct? I'm trying to solve it using the online integral calculator but it's not getting the answer.





Edit 1: Here are the changes and result I came up with



Edit 2: Fixed my calculation error and got a confident answer:
$$
P(t<X<Y)=int_t^inftyint_t^y lambda cdotmucdot
e^{-lambdacdot x-mucdot y}dxdy=frac{lambda}{lambda+mu}e^{-t(lambda+mu)}
$$



I would really appreciate if someone could check if this is correct. Thank you!










share|cite|improve this question











$endgroup$








  • 1




    $begingroup$
    Well, even without the help of online tools, you should be able to compute $$int_t^ylambda e^{-lambda x}dx$$ and to plug the result in the integral with respect to $x$...
    $endgroup$
    – Did
    Jan 11 at 16:11










  • $begingroup$
    Observe that $t < X < Y$ implies $t < Y$ and hence, the "domain of integration" (as Americans call it) is the set of $y$ such that $t < y.$ Having such a fix $y,$ the domain of integration of $X$ is simply $t < x < y.$ What I am expressing here is that your double integral is wrong.
    $endgroup$
    – Will M.
    Jan 11 at 16:51










  • $begingroup$
    @WillM. Since $t<y$, would the limit of the $dy$ integral be from t to $infty$?
    $endgroup$
    – hilageryolo
    Jan 11 at 20:03
















0












0








0





$begingroup$



What is $P(t lt X lt Y)$ for $tgt 0$, when X and Y are independent exponential variables with the parameters $lambda$ and $mu$ respectively?




Since X and Y are independent, I got joint PDF to be $lambda cdotmucdot
e^{-lambdacdot x-mucdot y}$
.



Now that I'm looking for $P(t lt X lt Y)$, using the joint PDF, I set it as:
$$
P(t<X<Y)=int_0^inftyint_t^y lambda cdotmucdot
e^{-lambdacdot x-mucdot y}dxdy
$$



Is this correct? I'm trying to solve it using the online integral calculator but it's not getting the answer.





Edit 1: Here are the changes and result I came up with



Edit 2: Fixed my calculation error and got a confident answer:
$$
P(t<X<Y)=int_t^inftyint_t^y lambda cdotmucdot
e^{-lambdacdot x-mucdot y}dxdy=frac{lambda}{lambda+mu}e^{-t(lambda+mu)}
$$



I would really appreciate if someone could check if this is correct. Thank you!










share|cite|improve this question











$endgroup$





What is $P(t lt X lt Y)$ for $tgt 0$, when X and Y are independent exponential variables with the parameters $lambda$ and $mu$ respectively?




Since X and Y are independent, I got joint PDF to be $lambda cdotmucdot
e^{-lambdacdot x-mucdot y}$
.



Now that I'm looking for $P(t lt X lt Y)$, using the joint PDF, I set it as:
$$
P(t<X<Y)=int_0^inftyint_t^y lambda cdotmucdot
e^{-lambdacdot x-mucdot y}dxdy
$$



Is this correct? I'm trying to solve it using the online integral calculator but it's not getting the answer.





Edit 1: Here are the changes and result I came up with



Edit 2: Fixed my calculation error and got a confident answer:
$$
P(t<X<Y)=int_t^inftyint_t^y lambda cdotmucdot
e^{-lambdacdot x-mucdot y}dxdy=frac{lambda}{lambda+mu}e^{-t(lambda+mu)}
$$



I would really appreciate if someone could check if this is correct. Thank you!







probability-theory probability-distributions






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share|cite|improve this question













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edited Jan 11 at 21:58







hilageryolo

















asked Jan 11 at 15:36









hilageryolohilageryolo

173




173








  • 1




    $begingroup$
    Well, even without the help of online tools, you should be able to compute $$int_t^ylambda e^{-lambda x}dx$$ and to plug the result in the integral with respect to $x$...
    $endgroup$
    – Did
    Jan 11 at 16:11










  • $begingroup$
    Observe that $t < X < Y$ implies $t < Y$ and hence, the "domain of integration" (as Americans call it) is the set of $y$ such that $t < y.$ Having such a fix $y,$ the domain of integration of $X$ is simply $t < x < y.$ What I am expressing here is that your double integral is wrong.
    $endgroup$
    – Will M.
    Jan 11 at 16:51










  • $begingroup$
    @WillM. Since $t<y$, would the limit of the $dy$ integral be from t to $infty$?
    $endgroup$
    – hilageryolo
    Jan 11 at 20:03
















  • 1




    $begingroup$
    Well, even without the help of online tools, you should be able to compute $$int_t^ylambda e^{-lambda x}dx$$ and to plug the result in the integral with respect to $x$...
    $endgroup$
    – Did
    Jan 11 at 16:11










  • $begingroup$
    Observe that $t < X < Y$ implies $t < Y$ and hence, the "domain of integration" (as Americans call it) is the set of $y$ such that $t < y.$ Having such a fix $y,$ the domain of integration of $X$ is simply $t < x < y.$ What I am expressing here is that your double integral is wrong.
    $endgroup$
    – Will M.
    Jan 11 at 16:51










  • $begingroup$
    @WillM. Since $t<y$, would the limit of the $dy$ integral be from t to $infty$?
    $endgroup$
    – hilageryolo
    Jan 11 at 20:03










1




1




$begingroup$
Well, even without the help of online tools, you should be able to compute $$int_t^ylambda e^{-lambda x}dx$$ and to plug the result in the integral with respect to $x$...
$endgroup$
– Did
Jan 11 at 16:11




$begingroup$
Well, even without the help of online tools, you should be able to compute $$int_t^ylambda e^{-lambda x}dx$$ and to plug the result in the integral with respect to $x$...
$endgroup$
– Did
Jan 11 at 16:11












$begingroup$
Observe that $t < X < Y$ implies $t < Y$ and hence, the "domain of integration" (as Americans call it) is the set of $y$ such that $t < y.$ Having such a fix $y,$ the domain of integration of $X$ is simply $t < x < y.$ What I am expressing here is that your double integral is wrong.
$endgroup$
– Will M.
Jan 11 at 16:51




$begingroup$
Observe that $t < X < Y$ implies $t < Y$ and hence, the "domain of integration" (as Americans call it) is the set of $y$ such that $t < y.$ Having such a fix $y,$ the domain of integration of $X$ is simply $t < x < y.$ What I am expressing here is that your double integral is wrong.
$endgroup$
– Will M.
Jan 11 at 16:51












$begingroup$
@WillM. Since $t<y$, would the limit of the $dy$ integral be from t to $infty$?
$endgroup$
– hilageryolo
Jan 11 at 20:03






$begingroup$
@WillM. Since $t<y$, would the limit of the $dy$ integral be from t to $infty$?
$endgroup$
– hilageryolo
Jan 11 at 20:03












1 Answer
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$begingroup$

Try this in Mathematica



Probability[ t < x < y, {x [Distributed] ExponentialDistribution[[Lambda]], y [Distributed] ExponentialDistribution[[Mu]]}]


You will get
$$
begin{array}{cc}
& left{
begin{array}{cc}
frac{lambda }{lambda +mu } & t<0 \
frac{lambda e^{-t (lambda +mu )}}{lambda +mu } & t ge 0 \
end{array}
right.
\
end{array}
$$






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    1 Answer
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    active

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    1 Answer
    1






    active

    oldest

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    active

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    0












    $begingroup$

    Try this in Mathematica



    Probability[ t < x < y, {x [Distributed] ExponentialDistribution[[Lambda]], y [Distributed] ExponentialDistribution[[Mu]]}]


    You will get
    $$
    begin{array}{cc}
    & left{
    begin{array}{cc}
    frac{lambda }{lambda +mu } & t<0 \
    frac{lambda e^{-t (lambda +mu )}}{lambda +mu } & t ge 0 \
    end{array}
    right.
    \
    end{array}
    $$






    share|cite|improve this answer









    $endgroup$


















      0












      $begingroup$

      Try this in Mathematica



      Probability[ t < x < y, {x [Distributed] ExponentialDistribution[[Lambda]], y [Distributed] ExponentialDistribution[[Mu]]}]


      You will get
      $$
      begin{array}{cc}
      & left{
      begin{array}{cc}
      frac{lambda }{lambda +mu } & t<0 \
      frac{lambda e^{-t (lambda +mu )}}{lambda +mu } & t ge 0 \
      end{array}
      right.
      \
      end{array}
      $$






      share|cite|improve this answer









      $endgroup$
















        0












        0








        0





        $begingroup$

        Try this in Mathematica



        Probability[ t < x < y, {x [Distributed] ExponentialDistribution[[Lambda]], y [Distributed] ExponentialDistribution[[Mu]]}]


        You will get
        $$
        begin{array}{cc}
        & left{
        begin{array}{cc}
        frac{lambda }{lambda +mu } & t<0 \
        frac{lambda e^{-t (lambda +mu )}}{lambda +mu } & t ge 0 \
        end{array}
        right.
        \
        end{array}
        $$






        share|cite|improve this answer









        $endgroup$



        Try this in Mathematica



        Probability[ t < x < y, {x [Distributed] ExponentialDistribution[[Lambda]], y [Distributed] ExponentialDistribution[[Mu]]}]


        You will get
        $$
        begin{array}{cc}
        & left{
        begin{array}{cc}
        frac{lambda }{lambda +mu } & t<0 \
        frac{lambda e^{-t (lambda +mu )}}{lambda +mu } & t ge 0 \
        end{array}
        right.
        \
        end{array}
        $$







        share|cite|improve this answer












        share|cite|improve this answer



        share|cite|improve this answer










        answered Jan 11 at 21:17









        ablmfablmf

        2,56842452




        2,56842452






























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