1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Marginal Probability Distribution

  1. Mar 12, 2017 #1
    1. The problem statement, all variables and given/known data
    Two components of a laptop computer have the following joint probability density function for their useful lifetimes X and Y (in years):

    f(xy)=xe^(−x(1+y)) 0 <= x <= y

    0 otherwise

    Find the marginal probability density function of X, fX(x). Enter a formula below. Use * for multiplication, / for division, ^ for power and exp for exponential function. For example, 3x^3*exp(-x/3) means 3x^3e^(-x/3).

    I found the answer to this, it is e^(-x).

    Find the marginal probability density function of Y, fY(y). Enter a formula below.

    I found the answer to this one too, its 1/(1 + y)^2 .

    What is the probability that the lifetime of at least one component exceeds 1 year (when the manufacturer's warranty expires)? Round your answer to 4 decimal places.

    This is the part I'm having trouble on, I'm not really sure how to start or set up this question.

    Thanks for the help.

    2. Relevant equations

    The marginal probability equations, I'm not sure how to write them here.

    3. The attempt at a solution
    I don't really know how to set up the third part.
  2. jcsd
  3. Mar 12, 2017 #2

    Ray Vickson

    User Avatar
    Science Advisor
    Homework Helper

    The complement of the event "at least one component has a lifetime of >= 1 year" is "both components have lifetimes < 1 year".
  4. Mar 12, 2017 #3

    Alright yeah that makes sense, the problem I have is how to set it up. Would I just do the double integral from 0 to 1 of the function with respect to x and y and then subtract?
    Last edited: Mar 12, 2017
  5. Mar 12, 2017 #4
    Actually nevermind I got it, thanks for the help!
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted