SOLUTION: A study of the amount of time it takes a specialist to repair a mobile MRI shows that the mean is 8.4 hours and the standard deviation is 1.8 hours. If 40 broken mobile MRIs are ra

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Question 1200753: A study of the amount of time it takes a specialist to repair a mobile MRI shows that the mean is 8.4 hours and the standard deviation is 1.8 hours. If 40 broken mobile MRIs are randomly selected, find
the probability that their mean repair time is less than 8.9 hours
Answer by Theo(13342) (Show Source):
You can put this solution on YOUR website!
population mean is = 8.4 with standard deviation of 1.8.
sample size is 40
standard error = standard deviation / square rooot of sample size = 1.8 / sqrt(40) = .2846049894.
z = (x-m)/s
z is the z-score
x is the test mean repair time of 8.9
m is the population mean of 8.4
s is the standard error.
formula becomes z = (8.9-8.4)/.2846049894 = 1.756820922.
probability of getting a z-score less that is equal to .960525876.
here's what it looks like on the calculator at https://davidmlane.com/hyperstat/z_table.html