Posted by pat on Tuesday, December 11, 2012 at 9:45pm.
6. Facebook reports that the average number of Facebook friends worldwide is 175.5 with a standard deviation of 90.57. If you were to take a sample of 25 students, what is the probability that the mean number Facebook friends in the sample will be 190 friends or more?

statistics  PsyDAG, Thursday, December 13, 2012 at 1:36am
Z = (scoremean)/SEm
SEm = SD/√n
Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportion/probability related to your Z score.

statistics  Joseph, Saturday, May 4, 2013 at 2:42am
Solution
My mean is 175.5
My standard deviation is=90.57
Sample=25
So the probability is
Formula to be used: P(X>190)=P((Xmean)/s
sqrt of my sample is = 5
(190175.5) / 90.57/5)
14.5 / 18.114
calculator says 0.8004858120790548746825659710721
I check the ztable and I see .8 under the z of 0.00 correlates to .2119
=0.2119
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