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Homework Help: Stats question , have work and answer shown

  1. Nov 6, 2008 #1
    1. The problem statement, all variables and given/known data

    i didnt know which forum stats is posted in so i posted it here, but the problem says the q is , Sheilas measure glucose level one hour after a sugary drink varies according to the normal distribution (u= 125 mg/dl) and r=10 mg/dl. What is the level L such that there is a probability only 0.05 that the mean glucose level of 4 test results falls above L?

    2. Relevant equations

    x= u(mew) + z*r

    3. The attempt at a solution
    I did a backwards normal calculation of x= 125 + .5199 (from table A probs) * 10 = 130.199

    i think its right but i dunno, does the 4 play a part in my equation or is this the wrong way to do it? ANY information would be helpful
  2. jcsd
  3. Nov 6, 2008 #2


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    Science Advisor

    Yes, it does. The average of n samples from a population with mean [itex]mu[/itex] and standard deviation [itex]\sigma[/itex] is normally distributed with mean [itex]mu[/itex] and standard deviation [itex]\sigma\sqrt{n}[/itex]. Notice that means that the larger sample you have the smaller its standard deviation is and the more "accurate" it is.
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