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Math Help - Expectation

  1. #1
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    Expectation

    The number of failures of a computer system in a week of operation has the following pmf:

    No of failures
    0
    1
    2
    3
    4
    5
    6
    Probability
    0.18
    0.28
    0.25
    0.18
    0.06
    0.04
    0.01

    (a)Find the expected number of failures in a week.
    (b)Find the variance of the number of failures in a week.

    a. I'm not sure if i solved this correctly: 0.18 + 1(.28)+2(.25)+3(.18)+4(.06)+5(.04)+6(.01) = 2 failures?
    b. (0-2)^2(.18)+ (1-2)^2(.28)+(2-2)^2(.25)+(3-2)^2(.18)+(4-2)^2(.06)+(5-2)^2(.04)+(6-2)^2(.01) = 1.94
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  2. #2
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    Quote Originally Posted by aaronrj View Post
    The number of failures of a computer system in a week of operation has the following pmf:

    No of failures

    0


    1


    2


    3


    4


    5


    6


    Probability
    0.18
    0.28
    0.25
    0.18
    0.06
    0.04
    0.01


    (a)Find the expected number of failures in a week.
    (b)Find the variance of the number of failures in a week.

    a. I'm not sure if i solved this correctly: 0.18 + 1(.28)+2(.25)+3(.18)+4(.06)+5(.04)+6(.01) = 2 failures?
    b. (0-2)^2(.18)+ (1-2)^2(.28)+(2-2)^2(.25)+(3-2)^2(.18)+(4-2)^2(.06)+(5-2)^2(.04)+(6-2)^2(.01) = 1.94
    I haven't checked the arithmetic but the approach is OK.
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