Question 507367
Among companies doing highway or bridge construction, 80% test employees for substance abuse (based on data from the Construction Financial Management
Association) 
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A study involves the random selection of 12 such companies.
Binomial Problem with n = 12 and p = 0.8
 
(a) Find the probability that exactly 7 of the 12 companies test for substance abuse.
P(x = 7) = 12C7(0.8)^7*(0.2)^5 = 0.0532
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(b) Find the probability that at least half of the companies test for substance abuse.
P(7<= x <=12) = 1 - P(0<= x <=6) 1 - binomcdf(12,0.8,6) = 0.9806
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(c) For a group of 12 companies, find the mean and standard deviation for the number (among 12) that test for substance abuse.
mean = np = 12*0.8 = 7.2
std = sqrt(npq) = sqrt(7.2*0.2) = 1.2 
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(d) Using the results from part (c) and the range rule of thumb, indentify the range of usual value.
If the "range of usual values" is 6*std, you get 6*1.2 = 7.2 
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Cheers,
Stan H.
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