SOLUTION: Am I doing the right thing? Please help me with this one. Replacement times for Nissan Almera automobiles are normally distributed with a mean of 7.1 years and a standard devia

Question 57670: Am I doing the right thing? Please help me with this one.
Replacement times for Nissan Almera automobiles are normally distributed with a mean of 7.1 years and a standard deviation of 4.1 years. Find the probability that seven randomly selected Nissan Almera have a mean replacement greater than 7 years. Please explain...
My solution:

z= x-u/o = 7-7.1/1.4= .0003
Thanks!
Answer by stanbon(75887) (Show Source): You can put this solution on YOUR website!
The standard deviation of the population is 4.1
but the standard deviation for samples of size
seven of the population is 4.1/sqrt(7)=1.5496
---------
So Prob(x-bar > 7)=Prob(z > (7-7.1)/1.5496)
=Prob(z> -0.0645)=0.5257...
Cheers,
Stan H.
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