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Help with understanding a solution in statistics

  1. Mar 29, 2015 #1

    "Fifty numbers are rounded-off to the nearest integer and the summed.
    Suppose that the individual round-off errors are uniformly distributed
    over (0:5; 0:5). What is the probability that the round-off error
    exceeds the exact sum by more than 3?"

    I don't understand how they calculate the variance where they get the 1/12

    This isn't homework nor am I taking a class in statistics. I will however be taking an exam in statistics so I can credit for a class in statistics in May. Any help will be appreciated.
  2. jcsd
  3. Mar 29, 2015 #2


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    The problem wording is rather bad and confusing. If I try to render what it should be, I get something like
    Your question where the ##\tfrac {1} {12}## comes from, can be answered with a simple: from the definition of the variance: calculate E[x2] for a uniform distribution.
    In your lecture suite: lecture 20.
  4. Mar 30, 2015 #3


    Staff: Mentor

    The interval should read "[-0.5, 0.5]".
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