Probability: joint probability distribution problem?

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Homework Help Overview

The problem involves determining the probability of an encounter between two individuals, John and George, who arrive at different times within specified intervals. John's arrival time is uniformly distributed between 12:00 and 12:15, while George's arrival time is uniformly distributed between 12:05 and 12:20. The challenge lies in understanding their waiting times and how these affect the probability of them meeting.

Discussion Character

  • Exploratory, Assumption checking, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the joint probability distribution of the arrival times and the implications of their respective waiting times. There is an exploration of the variable T, defined as the difference between George's and John's arrival times, and how this relates to the conditions for an encounter.

Discussion Status

Participants are actively engaging with the problem, clarifying the conditions under which an encounter occurs. Some have noted the relationship between the variables T and T2, and there is a recognition of the need to determine the probability density function (p.d.f) of T to calculate the required probability.

Contextual Notes

There is an emphasis on the constraints of the problem, particularly the specific waiting times for each individual and the uniform distributions of their arrival times. Participants are questioning how these factors influence the overall probability of an encounter.

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Homework Statement


John and George are set to meet each other at 12 o'clock. John's time of arrival, J, is distributed uniformly between 12:00 and 12:15. John will wait for George for 15 minutes. If he doesn't show up, he leaves. George's time of arrival, G, is also uniformly distributed, between 12:05 and 12:20. But he will only wait 5 minutes for John.

Find the probability of an encounter.

The Attempt at a Solution



I'm at complete lost with this problem. I think that what I have to do is find the jount probability distribution of J and G, but I couldn't say why. And the "waits for 15 minutes" thing also confuses me.

Any ideas?
 
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Hint: Let T=G-J. For what range of values of T will an encounter happen?
 
T between 0:00 and 0:05...

OK, and I have to do the same thing but considering T2 = J-G. How can I then find the entire answer? T+T2?
 
Note that T2 = -T, so it's essentially the same variable. In other words, if you have something like a<T2<b, that's the same as -a>T>-b. You only have to work with one variable. There's no need to work the cases out separately and combine them at the end.
 
No, no, I see. T has to be between -0:15 and 0:05, right? Because if G<J, T<0, and since J can only be 15 minutes earlier than G otherwise he leaves, T> -0:15. and if G>J, T>0, and since G can only be 5 minutes earlier than J, T<0:05.

So, what I'm looking for is P(-0:15<= T <= 0:05), right?
 
Right!
 
OK, thanks.
 
All understood.. but how to find out the p.d.f of T? Because without the pdf of T the required probability cannot be calculated..

Please help
 

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