# A study of 200 insomniacs paid for by the Serta Mattress Company - 6232

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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

Out of the 200 insomniacs, 98 reported regularly watching The Late Show with David Letterman before they began to count sheep.Calculate the margin of error for a 78% confidence interval of the true proportion of insomniacs who regularly watch David Letterman before counting sheep.

A.   0.056

B.   0.164

C.   0.136

D.   0.043

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:

=NORMSINV(0.89)

1.2265