Question 265568
The Bide-a-While efficiency hotel, which caters to business workers who stay for extended periods of time (weeks or months), offers room service. 
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The marketing director is interested in trying to determine whether or not she can advertise “room service in under 30 minutes, or the order is free”. 
You will be asked to identify how many delivery times she should sample to estimate the true mean delivery time to within 5 minutes at the 90% reliability level? Assume that the standard deviation for the delivery times is 18.2 minutes. 
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sample size = n = [z*s/E]^2
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sample size = n = [1.645*18.2/5]^2
n = 35.85
Rounding up: n = 36 times
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Cheers,
Stan H.