The probability of Bus A arriving before Bus B












1












$begingroup$


Bus A arrives at a random time between 2pm and 4pm, and Bus B arrives at a random time between 3pm and 5pm. What are the odds that Bus A arrives before Bus B?



My understanding is that since Bus B cannot possibly arrive between 2 and 3, we can only talk about the time between 3 and 4 pm, when there is an equal probability for both buses arriving. But in this case, the probability of Bus A arriving before B is 50%. No? What am I missing here? Or I should look at the entire timeline, 2 pm - 5 pm? But then in this case, it is still 50%. Where is my thinking wrong?










share|cite|improve this question









New contributor




IrinaS is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.







$endgroup$












  • $begingroup$
    Using conditional probability I think it must be. $P(A/B')$ proceeding from here gives us ans $1/22$ is it correct?
    $endgroup$
    – Vimath
    1 hour ago










  • $begingroup$
    Yes, the arrival of buses is independent events.
    $endgroup$
    – IrinaS
    58 mins ago
















1












$begingroup$


Bus A arrives at a random time between 2pm and 4pm, and Bus B arrives at a random time between 3pm and 5pm. What are the odds that Bus A arrives before Bus B?



My understanding is that since Bus B cannot possibly arrive between 2 and 3, we can only talk about the time between 3 and 4 pm, when there is an equal probability for both buses arriving. But in this case, the probability of Bus A arriving before B is 50%. No? What am I missing here? Or I should look at the entire timeline, 2 pm - 5 pm? But then in this case, it is still 50%. Where is my thinking wrong?










share|cite|improve this question









New contributor




IrinaS is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.







$endgroup$












  • $begingroup$
    Using conditional probability I think it must be. $P(A/B')$ proceeding from here gives us ans $1/22$ is it correct?
    $endgroup$
    – Vimath
    1 hour ago










  • $begingroup$
    Yes, the arrival of buses is independent events.
    $endgroup$
    – IrinaS
    58 mins ago














1












1








1





$begingroup$


Bus A arrives at a random time between 2pm and 4pm, and Bus B arrives at a random time between 3pm and 5pm. What are the odds that Bus A arrives before Bus B?



My understanding is that since Bus B cannot possibly arrive between 2 and 3, we can only talk about the time between 3 and 4 pm, when there is an equal probability for both buses arriving. But in this case, the probability of Bus A arriving before B is 50%. No? What am I missing here? Or I should look at the entire timeline, 2 pm - 5 pm? But then in this case, it is still 50%. Where is my thinking wrong?










share|cite|improve this question









New contributor




IrinaS is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.







$endgroup$




Bus A arrives at a random time between 2pm and 4pm, and Bus B arrives at a random time between 3pm and 5pm. What are the odds that Bus A arrives before Bus B?



My understanding is that since Bus B cannot possibly arrive between 2 and 3, we can only talk about the time between 3 and 4 pm, when there is an equal probability for both buses arriving. But in this case, the probability of Bus A arriving before B is 50%. No? What am I missing here? Or I should look at the entire timeline, 2 pm - 5 pm? But then in this case, it is still 50%. Where is my thinking wrong?







probability






share|cite|improve this question









New contributor




IrinaS is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.











share|cite|improve this question









New contributor




IrinaS is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.









share|cite|improve this question




share|cite|improve this question








edited 1 hour ago







IrinaS













New contributor




IrinaS is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.









asked 2 hours ago









IrinaSIrinaS

62




62




New contributor




IrinaS is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.





New contributor





IrinaS is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.






IrinaS is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.












  • $begingroup$
    Using conditional probability I think it must be. $P(A/B')$ proceeding from here gives us ans $1/22$ is it correct?
    $endgroup$
    – Vimath
    1 hour ago










  • $begingroup$
    Yes, the arrival of buses is independent events.
    $endgroup$
    – IrinaS
    58 mins ago


















  • $begingroup$
    Using conditional probability I think it must be. $P(A/B')$ proceeding from here gives us ans $1/22$ is it correct?
    $endgroup$
    – Vimath
    1 hour ago










  • $begingroup$
    Yes, the arrival of buses is independent events.
    $endgroup$
    – IrinaS
    58 mins ago
















$begingroup$
Using conditional probability I think it must be. $P(A/B')$ proceeding from here gives us ans $1/22$ is it correct?
$endgroup$
– Vimath
1 hour ago




$begingroup$
Using conditional probability I think it must be. $P(A/B')$ proceeding from here gives us ans $1/22$ is it correct?
$endgroup$
– Vimath
1 hour ago












$begingroup$
Yes, the arrival of buses is independent events.
$endgroup$
– IrinaS
58 mins ago




$begingroup$
Yes, the arrival of buses is independent events.
$endgroup$
– IrinaS
58 mins ago










3 Answers
3






active

oldest

votes


















3












$begingroup$

Let $A_e$ ($A$ early) be the event that $A$ arrives before $3$pm.



Let $B_ell$ be the event that $B$ arrives after $4$pm.



Let $C$ be the union : $C=A_e cup B_ell$.



Let $X$ be the event of interest ( $A$ arrives before $B$).



What we know (don't we?) that is $P(X | C)=1$ and $P(X | overline{C})=0.5$



Then we can write (total probability) $$P(X) = P(X cap C) + P(X capoverline{C})=P(X | C) P(C) + P(X mid overline{C})P(overline{C})$$



Can you go on from here ?






share|cite|improve this answer









$endgroup$













  • $begingroup$
    Sorry for the question. I am confused with 𝑃(𝑋|𝐶)=1. Here is why - A has already arrived before 4 pm, before 𝐵ℓ happens, right? Yes, B can arrive after 4 pm, but it does not make any difference for the question we are asking which is - the probability of A arriving before B, before 4 pm, because A arrive between 2 and 4.
    $endgroup$
    – IrinaS
    17 mins ago





















1












$begingroup$

Guide:



1) Draw rectangle $2le xle 4, 3le yle 5$, square $2le xle 3, 2le yle 3$ and line $y=x$.



2) The total area of the rectangle and square is $5$, so pdf is $1/5$.



3) Find total area of the square and rectangle above the line, which is $4.5$.



5) Finally, the required probability is $4.5cdot 1/5=9/10$.



Here is the graph:



$hspace{2cm}$enter image description here



Bus $A$ arriving before bus $B$:
$$A(2.5,4.5), B(3.5,4.5), C(2.5,3.5), D(3.4, 3.7), F(2.3,-), G(2.7,-).$$
Bus $A$ arriving after bus $B$:
$$E(3.7,3.3).$$






share|cite|improve this answer











$endgroup$













  • $begingroup$
    do we need the area above the x=y line, or below the line? I believe - under the line. Can you please clarify?
    $endgroup$
    – IrinaS
    28 mins ago



















0












$begingroup$

First, I’ll assume that the probability distribution of each bus’s arrival time is uniform in its range and independent. I think that’s implicit in the question but you don’t actually say so.



You’re mistaken when you say that if you know Bus A is arriving between $3$ and $4$, then there is an equal probability of either bus arriving first. There is a $50$% probability that Bus B arrives after $4$. The probabilities are equal only if you know that Bus A arrives between $3$ and $4$ and also that Bus B arrives between $3$ and $4$. That parlay occurs only $25$% of the time.



So $75$% of the time, you know that Bus A arrives first, and Bus A still arrives first half of the remaining $25$% of the time. Thus, the probability that Bus A arrives first is $87.5$%.






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
    });


    }
    });






    IrinaS is a new contributor. Be nice, and check out our Code of Conduct.










    draft saved

    draft discarded


















    StackExchange.ready(
    function () {
    StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fmath.stackexchange.com%2fquestions%2f3158927%2fthe-probability-of-bus-a-arriving-before-bus-b%23new-answer', 'question_page');
    }
    );

    Post as a guest















    Required, but never shown

























    3 Answers
    3






    active

    oldest

    votes








    3 Answers
    3






    active

    oldest

    votes









    active

    oldest

    votes






    active

    oldest

    votes









    3












    $begingroup$

    Let $A_e$ ($A$ early) be the event that $A$ arrives before $3$pm.



    Let $B_ell$ be the event that $B$ arrives after $4$pm.



    Let $C$ be the union : $C=A_e cup B_ell$.



    Let $X$ be the event of interest ( $A$ arrives before $B$).



    What we know (don't we?) that is $P(X | C)=1$ and $P(X | overline{C})=0.5$



    Then we can write (total probability) $$P(X) = P(X cap C) + P(X capoverline{C})=P(X | C) P(C) + P(X mid overline{C})P(overline{C})$$



    Can you go on from here ?






    share|cite|improve this answer









    $endgroup$













    • $begingroup$
      Sorry for the question. I am confused with 𝑃(𝑋|𝐶)=1. Here is why - A has already arrived before 4 pm, before 𝐵ℓ happens, right? Yes, B can arrive after 4 pm, but it does not make any difference for the question we are asking which is - the probability of A arriving before B, before 4 pm, because A arrive between 2 and 4.
      $endgroup$
      – IrinaS
      17 mins ago


















    3












    $begingroup$

    Let $A_e$ ($A$ early) be the event that $A$ arrives before $3$pm.



    Let $B_ell$ be the event that $B$ arrives after $4$pm.



    Let $C$ be the union : $C=A_e cup B_ell$.



    Let $X$ be the event of interest ( $A$ arrives before $B$).



    What we know (don't we?) that is $P(X | C)=1$ and $P(X | overline{C})=0.5$



    Then we can write (total probability) $$P(X) = P(X cap C) + P(X capoverline{C})=P(X | C) P(C) + P(X mid overline{C})P(overline{C})$$



    Can you go on from here ?






    share|cite|improve this answer









    $endgroup$













    • $begingroup$
      Sorry for the question. I am confused with 𝑃(𝑋|𝐶)=1. Here is why - A has already arrived before 4 pm, before 𝐵ℓ happens, right? Yes, B can arrive after 4 pm, but it does not make any difference for the question we are asking which is - the probability of A arriving before B, before 4 pm, because A arrive between 2 and 4.
      $endgroup$
      – IrinaS
      17 mins ago
















    3












    3








    3





    $begingroup$

    Let $A_e$ ($A$ early) be the event that $A$ arrives before $3$pm.



    Let $B_ell$ be the event that $B$ arrives after $4$pm.



    Let $C$ be the union : $C=A_e cup B_ell$.



    Let $X$ be the event of interest ( $A$ arrives before $B$).



    What we know (don't we?) that is $P(X | C)=1$ and $P(X | overline{C})=0.5$



    Then we can write (total probability) $$P(X) = P(X cap C) + P(X capoverline{C})=P(X | C) P(C) + P(X mid overline{C})P(overline{C})$$



    Can you go on from here ?






    share|cite|improve this answer









    $endgroup$



    Let $A_e$ ($A$ early) be the event that $A$ arrives before $3$pm.



    Let $B_ell$ be the event that $B$ arrives after $4$pm.



    Let $C$ be the union : $C=A_e cup B_ell$.



    Let $X$ be the event of interest ( $A$ arrives before $B$).



    What we know (don't we?) that is $P(X | C)=1$ and $P(X | overline{C})=0.5$



    Then we can write (total probability) $$P(X) = P(X cap C) + P(X capoverline{C})=P(X | C) P(C) + P(X mid overline{C})P(overline{C})$$



    Can you go on from here ?







    share|cite|improve this answer












    share|cite|improve this answer



    share|cite|improve this answer










    answered 1 hour ago









    leonbloyleonbloy

    41.8k647108




    41.8k647108












    • $begingroup$
      Sorry for the question. I am confused with 𝑃(𝑋|𝐶)=1. Here is why - A has already arrived before 4 pm, before 𝐵ℓ happens, right? Yes, B can arrive after 4 pm, but it does not make any difference for the question we are asking which is - the probability of A arriving before B, before 4 pm, because A arrive between 2 and 4.
      $endgroup$
      – IrinaS
      17 mins ago




















    • $begingroup$
      Sorry for the question. I am confused with 𝑃(𝑋|𝐶)=1. Here is why - A has already arrived before 4 pm, before 𝐵ℓ happens, right? Yes, B can arrive after 4 pm, but it does not make any difference for the question we are asking which is - the probability of A arriving before B, before 4 pm, because A arrive between 2 and 4.
      $endgroup$
      – IrinaS
      17 mins ago


















    $begingroup$
    Sorry for the question. I am confused with 𝑃(𝑋|𝐶)=1. Here is why - A has already arrived before 4 pm, before 𝐵ℓ happens, right? Yes, B can arrive after 4 pm, but it does not make any difference for the question we are asking which is - the probability of A arriving before B, before 4 pm, because A arrive between 2 and 4.
    $endgroup$
    – IrinaS
    17 mins ago






    $begingroup$
    Sorry for the question. I am confused with 𝑃(𝑋|𝐶)=1. Here is why - A has already arrived before 4 pm, before 𝐵ℓ happens, right? Yes, B can arrive after 4 pm, but it does not make any difference for the question we are asking which is - the probability of A arriving before B, before 4 pm, because A arrive between 2 and 4.
    $endgroup$
    – IrinaS
    17 mins ago













    1












    $begingroup$

    Guide:



    1) Draw rectangle $2le xle 4, 3le yle 5$, square $2le xle 3, 2le yle 3$ and line $y=x$.



    2) The total area of the rectangle and square is $5$, so pdf is $1/5$.



    3) Find total area of the square and rectangle above the line, which is $4.5$.



    5) Finally, the required probability is $4.5cdot 1/5=9/10$.



    Here is the graph:



    $hspace{2cm}$enter image description here



    Bus $A$ arriving before bus $B$:
    $$A(2.5,4.5), B(3.5,4.5), C(2.5,3.5), D(3.4, 3.7), F(2.3,-), G(2.7,-).$$
    Bus $A$ arriving after bus $B$:
    $$E(3.7,3.3).$$






    share|cite|improve this answer











    $endgroup$













    • $begingroup$
      do we need the area above the x=y line, or below the line? I believe - under the line. Can you please clarify?
      $endgroup$
      – IrinaS
      28 mins ago
















    1












    $begingroup$

    Guide:



    1) Draw rectangle $2le xle 4, 3le yle 5$, square $2le xle 3, 2le yle 3$ and line $y=x$.



    2) The total area of the rectangle and square is $5$, so pdf is $1/5$.



    3) Find total area of the square and rectangle above the line, which is $4.5$.



    5) Finally, the required probability is $4.5cdot 1/5=9/10$.



    Here is the graph:



    $hspace{2cm}$enter image description here



    Bus $A$ arriving before bus $B$:
    $$A(2.5,4.5), B(3.5,4.5), C(2.5,3.5), D(3.4, 3.7), F(2.3,-), G(2.7,-).$$
    Bus $A$ arriving after bus $B$:
    $$E(3.7,3.3).$$






    share|cite|improve this answer











    $endgroup$













    • $begingroup$
      do we need the area above the x=y line, or below the line? I believe - under the line. Can you please clarify?
      $endgroup$
      – IrinaS
      28 mins ago














    1












    1








    1





    $begingroup$

    Guide:



    1) Draw rectangle $2le xle 4, 3le yle 5$, square $2le xle 3, 2le yle 3$ and line $y=x$.



    2) The total area of the rectangle and square is $5$, so pdf is $1/5$.



    3) Find total area of the square and rectangle above the line, which is $4.5$.



    5) Finally, the required probability is $4.5cdot 1/5=9/10$.



    Here is the graph:



    $hspace{2cm}$enter image description here



    Bus $A$ arriving before bus $B$:
    $$A(2.5,4.5), B(3.5,4.5), C(2.5,3.5), D(3.4, 3.7), F(2.3,-), G(2.7,-).$$
    Bus $A$ arriving after bus $B$:
    $$E(3.7,3.3).$$






    share|cite|improve this answer











    $endgroup$



    Guide:



    1) Draw rectangle $2le xle 4, 3le yle 5$, square $2le xle 3, 2le yle 3$ and line $y=x$.



    2) The total area of the rectangle and square is $5$, so pdf is $1/5$.



    3) Find total area of the square and rectangle above the line, which is $4.5$.



    5) Finally, the required probability is $4.5cdot 1/5=9/10$.



    Here is the graph:



    $hspace{2cm}$enter image description here



    Bus $A$ arriving before bus $B$:
    $$A(2.5,4.5), B(3.5,4.5), C(2.5,3.5), D(3.4, 3.7), F(2.3,-), G(2.7,-).$$
    Bus $A$ arriving after bus $B$:
    $$E(3.7,3.3).$$







    share|cite|improve this answer














    share|cite|improve this answer



    share|cite|improve this answer








    edited 18 mins ago

























    answered 1 hour ago









    farruhotafarruhota

    21.4k2841




    21.4k2841












    • $begingroup$
      do we need the area above the x=y line, or below the line? I believe - under the line. Can you please clarify?
      $endgroup$
      – IrinaS
      28 mins ago


















    • $begingroup$
      do we need the area above the x=y line, or below the line? I believe - under the line. Can you please clarify?
      $endgroup$
      – IrinaS
      28 mins ago
















    $begingroup$
    do we need the area above the x=y line, or below the line? I believe - under the line. Can you please clarify?
    $endgroup$
    – IrinaS
    28 mins ago




    $begingroup$
    do we need the area above the x=y line, or below the line? I believe - under the line. Can you please clarify?
    $endgroup$
    – IrinaS
    28 mins ago











    0












    $begingroup$

    First, I’ll assume that the probability distribution of each bus’s arrival time is uniform in its range and independent. I think that’s implicit in the question but you don’t actually say so.



    You’re mistaken when you say that if you know Bus A is arriving between $3$ and $4$, then there is an equal probability of either bus arriving first. There is a $50$% probability that Bus B arrives after $4$. The probabilities are equal only if you know that Bus A arrives between $3$ and $4$ and also that Bus B arrives between $3$ and $4$. That parlay occurs only $25$% of the time.



    So $75$% of the time, you know that Bus A arrives first, and Bus A still arrives first half of the remaining $25$% of the time. Thus, the probability that Bus A arrives first is $87.5$%.






    share|cite|improve this answer









    $endgroup$


















      0












      $begingroup$

      First, I’ll assume that the probability distribution of each bus’s arrival time is uniform in its range and independent. I think that’s implicit in the question but you don’t actually say so.



      You’re mistaken when you say that if you know Bus A is arriving between $3$ and $4$, then there is an equal probability of either bus arriving first. There is a $50$% probability that Bus B arrives after $4$. The probabilities are equal only if you know that Bus A arrives between $3$ and $4$ and also that Bus B arrives between $3$ and $4$. That parlay occurs only $25$% of the time.



      So $75$% of the time, you know that Bus A arrives first, and Bus A still arrives first half of the remaining $25$% of the time. Thus, the probability that Bus A arrives first is $87.5$%.






      share|cite|improve this answer









      $endgroup$
















        0












        0








        0





        $begingroup$

        First, I’ll assume that the probability distribution of each bus’s arrival time is uniform in its range and independent. I think that’s implicit in the question but you don’t actually say so.



        You’re mistaken when you say that if you know Bus A is arriving between $3$ and $4$, then there is an equal probability of either bus arriving first. There is a $50$% probability that Bus B arrives after $4$. The probabilities are equal only if you know that Bus A arrives between $3$ and $4$ and also that Bus B arrives between $3$ and $4$. That parlay occurs only $25$% of the time.



        So $75$% of the time, you know that Bus A arrives first, and Bus A still arrives first half of the remaining $25$% of the time. Thus, the probability that Bus A arrives first is $87.5$%.






        share|cite|improve this answer









        $endgroup$



        First, I’ll assume that the probability distribution of each bus’s arrival time is uniform in its range and independent. I think that’s implicit in the question but you don’t actually say so.



        You’re mistaken when you say that if you know Bus A is arriving between $3$ and $4$, then there is an equal probability of either bus arriving first. There is a $50$% probability that Bus B arrives after $4$. The probabilities are equal only if you know that Bus A arrives between $3$ and $4$ and also that Bus B arrives between $3$ and $4$. That parlay occurs only $25$% of the time.



        So $75$% of the time, you know that Bus A arrives first, and Bus A still arrives first half of the remaining $25$% of the time. Thus, the probability that Bus A arrives first is $87.5$%.







        share|cite|improve this answer












        share|cite|improve this answer



        share|cite|improve this answer










        answered 1 hour ago









        Robert ShoreRobert Shore

        3,410323




        3,410323






















            IrinaS is a new contributor. Be nice, and check out our Code of Conduct.










            draft saved

            draft discarded


















            IrinaS is a new contributor. Be nice, and check out our Code of Conduct.













            IrinaS is a new contributor. Be nice, and check out our Code of Conduct.












            IrinaS is a new contributor. Be nice, and check out our Code of Conduct.
















            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%2f3158927%2fthe-probability-of-bus-a-arriving-before-bus-b%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

            A CLEAN and SIMPLE way to add appendices to Table of Contents and bookmarks

            Calculate evaluation metrics using cross_val_predict sklearn

            Insert data from modal to MySQL (multiple modal on website)