$X sim Exp(frac{1}{3}) $ If $Y= max(X,2)$ Find $E(Y)$












1












$begingroup$


$X sim Exp(frac{1}{3}) $



If $Y= max(X,2)$ Find $E(Y)$



I did in two ways can anyone point out my mistake ?



First one



$f(y)=
begin{cases}
2, & text{if $0<xle2$ } \[2ex]
X, & text{if $2<x<infty$ }
end{cases}$



$E(Y)=E(Y|0<x<2)P(0<xle2)+E(Y|2<x<infty)P(2<x<infty)$



$E(Y)=2(1-e^{frac{2}{3}})+e^{frac{-2}{3}}int dfrac{x}{3}e^{-frac{x}{3}} dx=2(1-e^{frac{2}{3}})+dfrac{e^{frac{-2}{3}}}{3}bigg(bigg(-3xe^{-frac{x}{3}}bigg)_{2}^{infty}-bigg(9e^{-frac{x}{3}}bigg)_{2}^{infty}bigg)=2-2e^{frac{-2}{3}}+dfrac{e^{frac{-2}{3}}}{3}bigg(bigg(6e^{-frac{2}{3}}bigg)+bigg(9e^{-frac{2}{3}}bigg)bigg)=2-2e^{-frac{2}{3}}+5e^{-frac{4}{3}}$



Second way



$E(Y)=int max(X,2)f(x)dx=int_0^{2} 2f(x)dx+int _{2}^{infty}xf(x)dx=2(1-e^{frac{-2}{3}})+bigg(bigg(-3xe^{-frac{x}{3}}bigg)_{2}^{infty}-bigg(9e^{-frac{x}{3}}bigg)_{2}^{infty}bigg)=2-2^{-frac{2}{3}}+5e^{-frac{2}{3}}=2+3e^{-frac{2}{3}}$



Now I am not sure which of them is correct and why can anyone tell me ?










share|cite|improve this question











$endgroup$








  • 1




    $begingroup$
    You meant find $E[Y]$, right?
    $endgroup$
    – Keen-ameteur
    Jan 28 at 13:36










  • $begingroup$
    @keen-ameteur yes I am sorry.
    $endgroup$
    – Daman deep
    Jan 28 at 13:40
















1












$begingroup$


$X sim Exp(frac{1}{3}) $



If $Y= max(X,2)$ Find $E(Y)$



I did in two ways can anyone point out my mistake ?



First one



$f(y)=
begin{cases}
2, & text{if $0<xle2$ } \[2ex]
X, & text{if $2<x<infty$ }
end{cases}$



$E(Y)=E(Y|0<x<2)P(0<xle2)+E(Y|2<x<infty)P(2<x<infty)$



$E(Y)=2(1-e^{frac{2}{3}})+e^{frac{-2}{3}}int dfrac{x}{3}e^{-frac{x}{3}} dx=2(1-e^{frac{2}{3}})+dfrac{e^{frac{-2}{3}}}{3}bigg(bigg(-3xe^{-frac{x}{3}}bigg)_{2}^{infty}-bigg(9e^{-frac{x}{3}}bigg)_{2}^{infty}bigg)=2-2e^{frac{-2}{3}}+dfrac{e^{frac{-2}{3}}}{3}bigg(bigg(6e^{-frac{2}{3}}bigg)+bigg(9e^{-frac{2}{3}}bigg)bigg)=2-2e^{-frac{2}{3}}+5e^{-frac{4}{3}}$



Second way



$E(Y)=int max(X,2)f(x)dx=int_0^{2} 2f(x)dx+int _{2}^{infty}xf(x)dx=2(1-e^{frac{-2}{3}})+bigg(bigg(-3xe^{-frac{x}{3}}bigg)_{2}^{infty}-bigg(9e^{-frac{x}{3}}bigg)_{2}^{infty}bigg)=2-2^{-frac{2}{3}}+5e^{-frac{2}{3}}=2+3e^{-frac{2}{3}}$



Now I am not sure which of them is correct and why can anyone tell me ?










share|cite|improve this question











$endgroup$








  • 1




    $begingroup$
    You meant find $E[Y]$, right?
    $endgroup$
    – Keen-ameteur
    Jan 28 at 13:36










  • $begingroup$
    @keen-ameteur yes I am sorry.
    $endgroup$
    – Daman deep
    Jan 28 at 13:40














1












1








1





$begingroup$


$X sim Exp(frac{1}{3}) $



If $Y= max(X,2)$ Find $E(Y)$



I did in two ways can anyone point out my mistake ?



First one



$f(y)=
begin{cases}
2, & text{if $0<xle2$ } \[2ex]
X, & text{if $2<x<infty$ }
end{cases}$



$E(Y)=E(Y|0<x<2)P(0<xle2)+E(Y|2<x<infty)P(2<x<infty)$



$E(Y)=2(1-e^{frac{2}{3}})+e^{frac{-2}{3}}int dfrac{x}{3}e^{-frac{x}{3}} dx=2(1-e^{frac{2}{3}})+dfrac{e^{frac{-2}{3}}}{3}bigg(bigg(-3xe^{-frac{x}{3}}bigg)_{2}^{infty}-bigg(9e^{-frac{x}{3}}bigg)_{2}^{infty}bigg)=2-2e^{frac{-2}{3}}+dfrac{e^{frac{-2}{3}}}{3}bigg(bigg(6e^{-frac{2}{3}}bigg)+bigg(9e^{-frac{2}{3}}bigg)bigg)=2-2e^{-frac{2}{3}}+5e^{-frac{4}{3}}$



Second way



$E(Y)=int max(X,2)f(x)dx=int_0^{2} 2f(x)dx+int _{2}^{infty}xf(x)dx=2(1-e^{frac{-2}{3}})+bigg(bigg(-3xe^{-frac{x}{3}}bigg)_{2}^{infty}-bigg(9e^{-frac{x}{3}}bigg)_{2}^{infty}bigg)=2-2^{-frac{2}{3}}+5e^{-frac{2}{3}}=2+3e^{-frac{2}{3}}$



Now I am not sure which of them is correct and why can anyone tell me ?










share|cite|improve this question











$endgroup$




$X sim Exp(frac{1}{3}) $



If $Y= max(X,2)$ Find $E(Y)$



I did in two ways can anyone point out my mistake ?



First one



$f(y)=
begin{cases}
2, & text{if $0<xle2$ } \[2ex]
X, & text{if $2<x<infty$ }
end{cases}$



$E(Y)=E(Y|0<x<2)P(0<xle2)+E(Y|2<x<infty)P(2<x<infty)$



$E(Y)=2(1-e^{frac{2}{3}})+e^{frac{-2}{3}}int dfrac{x}{3}e^{-frac{x}{3}} dx=2(1-e^{frac{2}{3}})+dfrac{e^{frac{-2}{3}}}{3}bigg(bigg(-3xe^{-frac{x}{3}}bigg)_{2}^{infty}-bigg(9e^{-frac{x}{3}}bigg)_{2}^{infty}bigg)=2-2e^{frac{-2}{3}}+dfrac{e^{frac{-2}{3}}}{3}bigg(bigg(6e^{-frac{2}{3}}bigg)+bigg(9e^{-frac{2}{3}}bigg)bigg)=2-2e^{-frac{2}{3}}+5e^{-frac{4}{3}}$



Second way



$E(Y)=int max(X,2)f(x)dx=int_0^{2} 2f(x)dx+int _{2}^{infty}xf(x)dx=2(1-e^{frac{-2}{3}})+bigg(bigg(-3xe^{-frac{x}{3}}bigg)_{2}^{infty}-bigg(9e^{-frac{x}{3}}bigg)_{2}^{infty}bigg)=2-2^{-frac{2}{3}}+5e^{-frac{2}{3}}=2+3e^{-frac{2}{3}}$



Now I am not sure which of them is correct and why can anyone tell me ?







probability statistics






share|cite|improve this question















share|cite|improve this question













share|cite|improve this question




share|cite|improve this question








edited Jan 28 at 13:40







Daman deep

















asked Jan 28 at 13:07









Daman deepDaman deep

756419




756419








  • 1




    $begingroup$
    You meant find $E[Y]$, right?
    $endgroup$
    – Keen-ameteur
    Jan 28 at 13:36










  • $begingroup$
    @keen-ameteur yes I am sorry.
    $endgroup$
    – Daman deep
    Jan 28 at 13:40














  • 1




    $begingroup$
    You meant find $E[Y]$, right?
    $endgroup$
    – Keen-ameteur
    Jan 28 at 13:36










  • $begingroup$
    @keen-ameteur yes I am sorry.
    $endgroup$
    – Daman deep
    Jan 28 at 13:40








1




1




$begingroup$
You meant find $E[Y]$, right?
$endgroup$
– Keen-ameteur
Jan 28 at 13:36




$begingroup$
You meant find $E[Y]$, right?
$endgroup$
– Keen-ameteur
Jan 28 at 13:36












$begingroup$
@keen-ameteur yes I am sorry.
$endgroup$
– Daman deep
Jan 28 at 13:40




$begingroup$
@keen-ameteur yes I am sorry.
$endgroup$
– Daman deep
Jan 28 at 13:40










2 Answers
2






active

oldest

votes


















2












$begingroup$

In the first method, you are using the law of total expectation, namely $E(Y)=E,[E(Ymid X)]$.



Note that



begin{align}
E(Y)&=E(Ymid Xle 2)P(Xle 2)+E(Ymid X>2)P(X>2)
\&=E(2mid Xle 2)P(Xle 2)+E(Xmid X>2)P(X>2)
\&=2P(Xle 2)+E(Xmathbf1_{X>2})tag{1}
end{align}



In the second approach, you are using this theorem to calculate
expected value of any function of $X$ directly. I would suggest using this method here.



begin{align}
E(max(X,2))&=frac{1}{3}int max(x,2)e^{-x/3}mathbf1_{x>0},dx
\&=frac{2}{3}int_0^2 e^{-x/3},dx+frac{1}{3}int_2^infty xe^{-x/3},dxtag{2}
end{align}



$(1)$ and $(2)$ are saying the same thing of course.



Integrating by parts the second integral, indeed we get $E(Y)=2+3e^{-2/3}$






share|cite|improve this answer











$endgroup$













  • $begingroup$
    I did solve it by parts. Is it wrong ?
    $endgroup$
    – Daman deep
    Jan 28 at 14:13










  • $begingroup$
    @Damandeep Your final answer is correct.
    $endgroup$
    – StubbornAtom
    Jan 28 at 14:16










  • $begingroup$
    Can you tell me in first method what went wrong? I am not able to find mistake. I solved it two three times. There is something wrong .
    $endgroup$
    – Daman deep
    Jan 28 at 14:18






  • 1




    $begingroup$
    @Damandeep If you want, in the first method you can use the memoryless property of exponential distribution to say that $E(Xmid X>2)=2+E(X)=2+3=5$. That gives you the answer quickly in fact.
    $endgroup$
    – StubbornAtom
    Jan 28 at 14:34








  • 1




    $begingroup$
    oh yes, I calculated it carelessly didn't apply the proper definition of conditional expectation. Thanks, man. That was it!
    $endgroup$
    – Daman deep
    Jan 28 at 15:14



















0












$begingroup$

This is how I would proceed (similar to your second method):



$E(Y)=int_0^22timesfrac{1}{3}e^{frac{-x}{3}}dx + int_2^infty xtimesfrac{1}{3}e^{frac{-x}{3}}dx$



$=2(1-e^{frac{-2}{3}}) +3int_frac{2}{3}^infty ttimes e^{-t}dt$



$=2(1-e^{frac{-2}{3}}) +3Gamma(2,frac{2}{3})$



$=2+3e^{frac{-2}{3}}$



Here is an easy tutorial to solve the incomplete Gamma Integral http://mathworld.wolfram.com/IncompleteGammaFunction.html






share|cite|improve this answer











$endgroup$














    Your Answer





    StackExchange.ifUsing("editor", function () {
    return StackExchange.using("mathjaxEditing", function () {
    StackExchange.MarkdownEditor.creationCallbacks.add(function (editor, postfix) {
    StackExchange.mathjaxEditing.prepareWmdForMathJax(editor, postfix, [["$", "$"], ["\\(","\\)"]]);
    });
    });
    }, "mathjax-editing");

    StackExchange.ready(function() {
    var channelOptions = {
    tags: "".split(" "),
    id: "69"
    };
    initTagRenderer("".split(" "), "".split(" "), channelOptions);

    StackExchange.using("externalEditor", function() {
    // Have to fire editor after snippets, if snippets enabled
    if (StackExchange.settings.snippets.snippetsEnabled) {
    StackExchange.using("snippets", function() {
    createEditor();
    });
    }
    else {
    createEditor();
    }
    });

    function createEditor() {
    StackExchange.prepareEditor({
    heartbeatType: 'answer',
    autoActivateHeartbeat: false,
    convertImagesToLinks: true,
    noModals: true,
    showLowRepImageUploadWarning: true,
    reputationToPostImages: 10,
    bindNavPrevention: true,
    postfix: "",
    imageUploader: {
    brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
    contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
    allowUrls: true
    },
    noCode: true, onDemand: true,
    discardSelector: ".discard-answer"
    ,immediatelyShowMarkdownHelp:true
    });


    }
    });














    draft saved

    draft discarded


















    StackExchange.ready(
    function () {
    StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fmath.stackexchange.com%2fquestions%2f3090831%2fx-sim-exp-frac13-if-y-maxx-2-find-ey%23new-answer', 'question_page');
    }
    );

    Post as a guest















    Required, but never shown

























    2 Answers
    2






    active

    oldest

    votes








    2 Answers
    2






    active

    oldest

    votes









    active

    oldest

    votes






    active

    oldest

    votes









    2












    $begingroup$

    In the first method, you are using the law of total expectation, namely $E(Y)=E,[E(Ymid X)]$.



    Note that



    begin{align}
    E(Y)&=E(Ymid Xle 2)P(Xle 2)+E(Ymid X>2)P(X>2)
    \&=E(2mid Xle 2)P(Xle 2)+E(Xmid X>2)P(X>2)
    \&=2P(Xle 2)+E(Xmathbf1_{X>2})tag{1}
    end{align}



    In the second approach, you are using this theorem to calculate
    expected value of any function of $X$ directly. I would suggest using this method here.



    begin{align}
    E(max(X,2))&=frac{1}{3}int max(x,2)e^{-x/3}mathbf1_{x>0},dx
    \&=frac{2}{3}int_0^2 e^{-x/3},dx+frac{1}{3}int_2^infty xe^{-x/3},dxtag{2}
    end{align}



    $(1)$ and $(2)$ are saying the same thing of course.



    Integrating by parts the second integral, indeed we get $E(Y)=2+3e^{-2/3}$






    share|cite|improve this answer











    $endgroup$













    • $begingroup$
      I did solve it by parts. Is it wrong ?
      $endgroup$
      – Daman deep
      Jan 28 at 14:13










    • $begingroup$
      @Damandeep Your final answer is correct.
      $endgroup$
      – StubbornAtom
      Jan 28 at 14:16










    • $begingroup$
      Can you tell me in first method what went wrong? I am not able to find mistake. I solved it two three times. There is something wrong .
      $endgroup$
      – Daman deep
      Jan 28 at 14:18






    • 1




      $begingroup$
      @Damandeep If you want, in the first method you can use the memoryless property of exponential distribution to say that $E(Xmid X>2)=2+E(X)=2+3=5$. That gives you the answer quickly in fact.
      $endgroup$
      – StubbornAtom
      Jan 28 at 14:34








    • 1




      $begingroup$
      oh yes, I calculated it carelessly didn't apply the proper definition of conditional expectation. Thanks, man. That was it!
      $endgroup$
      – Daman deep
      Jan 28 at 15:14
















    2












    $begingroup$

    In the first method, you are using the law of total expectation, namely $E(Y)=E,[E(Ymid X)]$.



    Note that



    begin{align}
    E(Y)&=E(Ymid Xle 2)P(Xle 2)+E(Ymid X>2)P(X>2)
    \&=E(2mid Xle 2)P(Xle 2)+E(Xmid X>2)P(X>2)
    \&=2P(Xle 2)+E(Xmathbf1_{X>2})tag{1}
    end{align}



    In the second approach, you are using this theorem to calculate
    expected value of any function of $X$ directly. I would suggest using this method here.



    begin{align}
    E(max(X,2))&=frac{1}{3}int max(x,2)e^{-x/3}mathbf1_{x>0},dx
    \&=frac{2}{3}int_0^2 e^{-x/3},dx+frac{1}{3}int_2^infty xe^{-x/3},dxtag{2}
    end{align}



    $(1)$ and $(2)$ are saying the same thing of course.



    Integrating by parts the second integral, indeed we get $E(Y)=2+3e^{-2/3}$






    share|cite|improve this answer











    $endgroup$













    • $begingroup$
      I did solve it by parts. Is it wrong ?
      $endgroup$
      – Daman deep
      Jan 28 at 14:13










    • $begingroup$
      @Damandeep Your final answer is correct.
      $endgroup$
      – StubbornAtom
      Jan 28 at 14:16










    • $begingroup$
      Can you tell me in first method what went wrong? I am not able to find mistake. I solved it two three times. There is something wrong .
      $endgroup$
      – Daman deep
      Jan 28 at 14:18






    • 1




      $begingroup$
      @Damandeep If you want, in the first method you can use the memoryless property of exponential distribution to say that $E(Xmid X>2)=2+E(X)=2+3=5$. That gives you the answer quickly in fact.
      $endgroup$
      – StubbornAtom
      Jan 28 at 14:34








    • 1




      $begingroup$
      oh yes, I calculated it carelessly didn't apply the proper definition of conditional expectation. Thanks, man. That was it!
      $endgroup$
      – Daman deep
      Jan 28 at 15:14














    2












    2








    2





    $begingroup$

    In the first method, you are using the law of total expectation, namely $E(Y)=E,[E(Ymid X)]$.



    Note that



    begin{align}
    E(Y)&=E(Ymid Xle 2)P(Xle 2)+E(Ymid X>2)P(X>2)
    \&=E(2mid Xle 2)P(Xle 2)+E(Xmid X>2)P(X>2)
    \&=2P(Xle 2)+E(Xmathbf1_{X>2})tag{1}
    end{align}



    In the second approach, you are using this theorem to calculate
    expected value of any function of $X$ directly. I would suggest using this method here.



    begin{align}
    E(max(X,2))&=frac{1}{3}int max(x,2)e^{-x/3}mathbf1_{x>0},dx
    \&=frac{2}{3}int_0^2 e^{-x/3},dx+frac{1}{3}int_2^infty xe^{-x/3},dxtag{2}
    end{align}



    $(1)$ and $(2)$ are saying the same thing of course.



    Integrating by parts the second integral, indeed we get $E(Y)=2+3e^{-2/3}$






    share|cite|improve this answer











    $endgroup$



    In the first method, you are using the law of total expectation, namely $E(Y)=E,[E(Ymid X)]$.



    Note that



    begin{align}
    E(Y)&=E(Ymid Xle 2)P(Xle 2)+E(Ymid X>2)P(X>2)
    \&=E(2mid Xle 2)P(Xle 2)+E(Xmid X>2)P(X>2)
    \&=2P(Xle 2)+E(Xmathbf1_{X>2})tag{1}
    end{align}



    In the second approach, you are using this theorem to calculate
    expected value of any function of $X$ directly. I would suggest using this method here.



    begin{align}
    E(max(X,2))&=frac{1}{3}int max(x,2)e^{-x/3}mathbf1_{x>0},dx
    \&=frac{2}{3}int_0^2 e^{-x/3},dx+frac{1}{3}int_2^infty xe^{-x/3},dxtag{2}
    end{align}



    $(1)$ and $(2)$ are saying the same thing of course.



    Integrating by parts the second integral, indeed we get $E(Y)=2+3e^{-2/3}$







    share|cite|improve this answer














    share|cite|improve this answer



    share|cite|improve this answer








    edited Jan 28 at 14:24

























    answered Jan 28 at 14:09









    StubbornAtomStubbornAtom

    6,30831440




    6,30831440












    • $begingroup$
      I did solve it by parts. Is it wrong ?
      $endgroup$
      – Daman deep
      Jan 28 at 14:13










    • $begingroup$
      @Damandeep Your final answer is correct.
      $endgroup$
      – StubbornAtom
      Jan 28 at 14:16










    • $begingroup$
      Can you tell me in first method what went wrong? I am not able to find mistake. I solved it two three times. There is something wrong .
      $endgroup$
      – Daman deep
      Jan 28 at 14:18






    • 1




      $begingroup$
      @Damandeep If you want, in the first method you can use the memoryless property of exponential distribution to say that $E(Xmid X>2)=2+E(X)=2+3=5$. That gives you the answer quickly in fact.
      $endgroup$
      – StubbornAtom
      Jan 28 at 14:34








    • 1




      $begingroup$
      oh yes, I calculated it carelessly didn't apply the proper definition of conditional expectation. Thanks, man. That was it!
      $endgroup$
      – Daman deep
      Jan 28 at 15:14


















    • $begingroup$
      I did solve it by parts. Is it wrong ?
      $endgroup$
      – Daman deep
      Jan 28 at 14:13










    • $begingroup$
      @Damandeep Your final answer is correct.
      $endgroup$
      – StubbornAtom
      Jan 28 at 14:16










    • $begingroup$
      Can you tell me in first method what went wrong? I am not able to find mistake. I solved it two three times. There is something wrong .
      $endgroup$
      – Daman deep
      Jan 28 at 14:18






    • 1




      $begingroup$
      @Damandeep If you want, in the first method you can use the memoryless property of exponential distribution to say that $E(Xmid X>2)=2+E(X)=2+3=5$. That gives you the answer quickly in fact.
      $endgroup$
      – StubbornAtom
      Jan 28 at 14:34








    • 1




      $begingroup$
      oh yes, I calculated it carelessly didn't apply the proper definition of conditional expectation. Thanks, man. That was it!
      $endgroup$
      – Daman deep
      Jan 28 at 15:14
















    $begingroup$
    I did solve it by parts. Is it wrong ?
    $endgroup$
    – Daman deep
    Jan 28 at 14:13




    $begingroup$
    I did solve it by parts. Is it wrong ?
    $endgroup$
    – Daman deep
    Jan 28 at 14:13












    $begingroup$
    @Damandeep Your final answer is correct.
    $endgroup$
    – StubbornAtom
    Jan 28 at 14:16




    $begingroup$
    @Damandeep Your final answer is correct.
    $endgroup$
    – StubbornAtom
    Jan 28 at 14:16












    $begingroup$
    Can you tell me in first method what went wrong? I am not able to find mistake. I solved it two three times. There is something wrong .
    $endgroup$
    – Daman deep
    Jan 28 at 14:18




    $begingroup$
    Can you tell me in first method what went wrong? I am not able to find mistake. I solved it two three times. There is something wrong .
    $endgroup$
    – Daman deep
    Jan 28 at 14:18




    1




    1




    $begingroup$
    @Damandeep If you want, in the first method you can use the memoryless property of exponential distribution to say that $E(Xmid X>2)=2+E(X)=2+3=5$. That gives you the answer quickly in fact.
    $endgroup$
    – StubbornAtom
    Jan 28 at 14:34






    $begingroup$
    @Damandeep If you want, in the first method you can use the memoryless property of exponential distribution to say that $E(Xmid X>2)=2+E(X)=2+3=5$. That gives you the answer quickly in fact.
    $endgroup$
    – StubbornAtom
    Jan 28 at 14:34






    1




    1




    $begingroup$
    oh yes, I calculated it carelessly didn't apply the proper definition of conditional expectation. Thanks, man. That was it!
    $endgroup$
    – Daman deep
    Jan 28 at 15:14




    $begingroup$
    oh yes, I calculated it carelessly didn't apply the proper definition of conditional expectation. Thanks, man. That was it!
    $endgroup$
    – Daman deep
    Jan 28 at 15:14











    0












    $begingroup$

    This is how I would proceed (similar to your second method):



    $E(Y)=int_0^22timesfrac{1}{3}e^{frac{-x}{3}}dx + int_2^infty xtimesfrac{1}{3}e^{frac{-x}{3}}dx$



    $=2(1-e^{frac{-2}{3}}) +3int_frac{2}{3}^infty ttimes e^{-t}dt$



    $=2(1-e^{frac{-2}{3}}) +3Gamma(2,frac{2}{3})$



    $=2+3e^{frac{-2}{3}}$



    Here is an easy tutorial to solve the incomplete Gamma Integral http://mathworld.wolfram.com/IncompleteGammaFunction.html






    share|cite|improve this answer











    $endgroup$


















      0












      $begingroup$

      This is how I would proceed (similar to your second method):



      $E(Y)=int_0^22timesfrac{1}{3}e^{frac{-x}{3}}dx + int_2^infty xtimesfrac{1}{3}e^{frac{-x}{3}}dx$



      $=2(1-e^{frac{-2}{3}}) +3int_frac{2}{3}^infty ttimes e^{-t}dt$



      $=2(1-e^{frac{-2}{3}}) +3Gamma(2,frac{2}{3})$



      $=2+3e^{frac{-2}{3}}$



      Here is an easy tutorial to solve the incomplete Gamma Integral http://mathworld.wolfram.com/IncompleteGammaFunction.html






      share|cite|improve this answer











      $endgroup$
















        0












        0








        0





        $begingroup$

        This is how I would proceed (similar to your second method):



        $E(Y)=int_0^22timesfrac{1}{3}e^{frac{-x}{3}}dx + int_2^infty xtimesfrac{1}{3}e^{frac{-x}{3}}dx$



        $=2(1-e^{frac{-2}{3}}) +3int_frac{2}{3}^infty ttimes e^{-t}dt$



        $=2(1-e^{frac{-2}{3}}) +3Gamma(2,frac{2}{3})$



        $=2+3e^{frac{-2}{3}}$



        Here is an easy tutorial to solve the incomplete Gamma Integral http://mathworld.wolfram.com/IncompleteGammaFunction.html






        share|cite|improve this answer











        $endgroup$



        This is how I would proceed (similar to your second method):



        $E(Y)=int_0^22timesfrac{1}{3}e^{frac{-x}{3}}dx + int_2^infty xtimesfrac{1}{3}e^{frac{-x}{3}}dx$



        $=2(1-e^{frac{-2}{3}}) +3int_frac{2}{3}^infty ttimes e^{-t}dt$



        $=2(1-e^{frac{-2}{3}}) +3Gamma(2,frac{2}{3})$



        $=2+3e^{frac{-2}{3}}$



        Here is an easy tutorial to solve the incomplete Gamma Integral http://mathworld.wolfram.com/IncompleteGammaFunction.html







        share|cite|improve this answer














        share|cite|improve this answer



        share|cite|improve this answer








        edited Jan 28 at 14:53

























        answered Jan 28 at 13:52









        s0ulr3aper07s0ulr3aper07

        580111




        580111






























            draft saved

            draft discarded




















































            Thanks for contributing an answer to Mathematics Stack Exchange!


            • Please be sure to answer the question. Provide details and share your research!

            But avoid



            • Asking for help, clarification, or responding to other answers.

            • Making statements based on opinion; back them up with references or personal experience.


            Use MathJax to format equations. MathJax reference.


            To learn more, see our tips on writing great answers.




            draft saved


            draft discarded














            StackExchange.ready(
            function () {
            StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fmath.stackexchange.com%2fquestions%2f3090831%2fx-sim-exp-frac13-if-y-maxx-2-find-ey%23new-answer', 'question_page');
            }
            );

            Post as a guest















            Required, but never shown





















































            Required, but never shown














            Required, but never shown












            Required, but never shown







            Required, but never shown

































            Required, but never shown














            Required, but never shown












            Required, but never shown







            Required, but never shown







            Popular posts from this blog

            MongoDB - Not Authorized To Execute Command

            How to fix TextFormField cause rebuild widget in Flutter

            in spring boot 2.1 many test slices are not allowed anymore due to multiple @BootstrapWith