Finding Probability Density Functions for Independent Random Variables

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SUMMARY

This discussion focuses on finding the probability density functions (PDFs) for independent random variables, specifically for uniformly distributed variables on the interval [0; a] and exponentially distributed variables. The first problem involves determining the PDF for the random variable z = x - y, where x and y are independent and uniformly distributed. The second problem addresses the same for exponentially distributed variables with the probability function p = exp(-x). Key insights include the importance of convolution in solving these problems and the distinction between cumulative distribution functions (CDFs) and PDFs, with a specific correction noted for the limits in the double integrals used in the calculations.

PREREQUISITES
  • Understanding of probability density functions (PDFs)
  • Knowledge of cumulative distribution functions (CDFs)
  • Familiarity with convolution in probability theory
  • Basic concepts of uniform and exponential distributions
NEXT STEPS
  • Study the concept of convolution in probability theory
  • Learn how to differentiate cumulative distribution functions to obtain probability density functions
  • Explore the properties of uniform distributions on intervals
  • Investigate the characteristics of exponential distributions and their applications
USEFUL FOR

Students studying probability theory, mathematicians working with random variables, and anyone interested in statistical analysis of independent random variables.

proton4ik
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Homework Statement


Hello! I'm trying to understand how to solve the following type of problems.

1) Random variables x and y are independent and uniformly distributed on the interval [0; a]. Find probability density function of a random variable z=x-y.

2) Exponentially distributed (p=exp(-x), x>=0) random variables x and y are independent. Find probability density function of a random variable z=x-y.

Homework Equations


Can someone please check if my attempt to solve the problems is successful or not? I'd appreciate any help :)

The Attempt at a Solution


(Attached file)

Thank you in advance[/B]
 

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Just a comment:
From the exercise I read they want you to find the probability distribution itself, not the accumulated function. A slightly different beast.

And a question:
Do you know about convolution ? (you are more or less working it out on your own here). Understanding that concept makes things a lot easier.
 
For part (1) your answer is correct for ##z\leq 0## but not for ##0<z<a##. If you substitute ##z=0## into your formula for that latter case you get 0, whereas it should be 1/2. I think the problem will be with the limits used in the inner of your double integrals. The probability should move smoothly from 1/2 to 1 as ##z## goes from 0 to ##a##.

EDIT: Just saw BvU's answer and I agree with that. Your answer is a CDF but a PDF has been requested. You can get the PDF by differentiating the CDF.
 

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