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!

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!!
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Discussions: Sums of Independent Random Variables