# A study of 200 insomniacs paid for by the Serta Mattress - 12944

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## mareya

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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±13.62

B.  350±13.56

C.  350±16.38

D.  350±10.41

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 120. An insomniac is a person who has difficulty falling asleep. Some useful numbers might be:

&nbs