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Sums of Independent Random Variables

  1. Aug 30, 2009 #1
    1. The problem statement, all variables and given/known data

    The distribution of the IQ of a randomly selected student from a certain college is N(110,16). What is the probability that the average of the IQ's of 10 randomly selected students from this college is at least 112?


    2. Relevant equations

    I think we need P(Sample Mean - 110 >= 2)


    3. The attempt at a solution

    My solution was Probability = (112-110)/1.6 = 1.25; 1-I(1.25)= 1-.8944 =.1056

    The answer in the book is .0571, so I know I'm going wrong somewhere.

    Any ideas?
     
  2. jcsd
  3. Aug 30, 2009 #2
    No need to respond, guys. I have found the error of my ways. I forgot that the std Error equals the std deviation divided by the sqr. root of the sample size. Working with that would have brought me to the Probability = 1-I(1.58) = 1-1.9429 =.0571. Thanks, anyway!!
     
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