Finding the Joint PMF of Two Independent Poisson Random Variables

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SUMMARY

The joint probability mass function (pmf) of two independent Poisson random variables, X ~ Pois(λ) and Y ~ Pois(μ), can be derived using the relationship between the variables. The pmf for X is given by px(k) = e^(-λ) * λ^k / k!, and for Y by py(k) = e^(-μ) * μ^k / k!. To find pX,X+Y(k,n), where X=k and X+Y=n, one must recognize that Y can be expressed as Y = n - k, leading to the joint pmf being pX,X+Y(k,n) = px(k) * py(n-k).

PREREQUISITES
  • Understanding of Poisson distribution and its properties
  • Familiarity with probability mass functions (pmf)
  • Knowledge of independent random variables
  • Basic algebra for manipulating equations
NEXT STEPS
  • Study the derivation of the joint pmf for independent random variables
  • Explore the properties of the Poisson distribution in depth
  • Learn about conditional probability and its application to joint distributions
  • Investigate the concept of convolution for independent random variables
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Students in statistics or probability theory, data scientists working with Poisson processes, and anyone studying joint distributions of random variables.

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Homework Statement



X~Pois(λ)=> px(k)=eλk/k!

Y~Pois(μ)=> py(k)=eμk/k!

Find pX,X+Y(k,n)=P(X=k, X+Y=n)

Homework Equations


...I know the pmf for X+Y ~ Pois(λ+μ)

The Attempt at a Solution


As I understand the joint pmf for two independent random variables would be the product of the two individual pmfs. However as X+Y is dependent on X I got really stuck trying to think about this one and how to set it up.

Any help would be great. Thanks :)
 
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If X=k and X+Y=n then Y=?
 

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