A study of 200 insomniacs paid for by the Serta Mattress Company - 6198

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A study of 200 insomniacs paid for by the Serta Mattress Company found that the average insomniac counted 350 sheep before falling asleep, with a standard deviation of 120. An insomniac is a person who has difficulty falling asleep. Some useful numbers might be: =NORMSINV(0.89) 1.2265 =NORMSINV(0.945) 1.5982 =TINV(0.89,199) 0.1385 =TINV(0.11,199) 1.6053 =TINV(0.055,199) 1.9302 Calculate an 89% confidence interval for the true mean number of sheep counted by insomniacs. 

A. 350±16.38 

B. 350±13.62 

C. 350±10.41 

D. 350±13.56 

 
Solution Description

A study of 200 insomniacs paid for by the Serta Mattress Company found that the average insomniac counted 350 sheep before falling asleep, with a standard deviation of