Question 200682
The accountant department at Weston Materials, inc, a national manufacturer of unattached garages, reports that it takes two construction workers a mean of 32 hours and a standard deviation of 2 hours to erect the Red Barn model Assume the assemble times follow the normal distribution. 
a) Determine the z values for 29 and 34 hours. What percent of the garage takes between 32 and 34 hours to erect?
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z(29) = (29-32)/2 = -3/2 = -1.5
z(34) = (34-32)/2 = 2/2 = 1
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b) What percent of the garage take between 29 hours and 34 hours to erect
P(29<x<34) = P(-1.5<z<1) = 0.7745 = 77.45%
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c) What percent of the garage takes between 28.7 hours or less erect?
Find the z-values of 28.7 and 0.
Then find the percentage between those two z values to get:
Ans: 4.95%
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d) Of the garage, 5 percent take how many hours or more to erect
The z value of 5% is -1.645
Find the x-value corresponding to z=-1.645
x = zs+u
x = -1.645*2 + 32
x = 28.71 hrs.
Ans: # of hours >= 28.71 
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Cheers,
Stan H.