SOLUTION: Production manager at a wall clock company wants to test their new clogs the designer claims they have a mean life of 14 years with a variance of 16 if the claim is true in the sam

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Question 1140379: Production manager at a wall clock company wants to test their new clogs the designer claims they have a mean life of 14 years with a variance of 16 if the claim is true in the sample of 40 clocks what is the probability that the mean clock life would be greater than 13.6 years

I'm having trouble figuring out what formula to use if I can figure out the formula I can figure out the question
Answer by Boreal(15235) About Me  (Show Source):
You can put this solution on YOUR website!
The formula you want is
z>(x bar-mean)/sd/sqrt(n), which becomes (x bar-mean)*sqrt(n)/sd
variance is 16, sd=4
so z> (13.6-14)*sqrt(40)/4
I would use z and not t here, because the designer claims a mean of 14 and sd 4, and the sample's sd is not considered here.