Question 116516
The accounting department @ Weston Materials, Inc. 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 assembly times follow the normal distribution. 
a)Determine the z values for 29 and 34 hours. What percent of the garages take between 32 and 34 hours to erect?
z(29) = (29-32)/2 = -1
z(34) = (34-32)/2 = 1
P(32<X<34) = P(0<z<1) = 0.34
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b)What percent of the garages take between 29 hours and 34 hours to erect?
P(29<X<34) = P(-1<z<1) = 0.68
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c)What percent of the garages take 28.7 hours or less to erect? 
Find the z-score of 28.7
z(28.7) = (28.7-32)/2 = -1.65
Find P(z < -1.65) = 0.0495
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d)Of the garages, 5 percent take how many hours or more to erect?
Find the z-value that has 0.05 of the population above it.
z = 1.6449
find the x-value associated with that z value:
1.6449 = (x-32)/2
x-32 = 3.2897
x = 35.2897
5% take 35.2897 or more hours to erect.
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Cheers,
Stan H.