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

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. 0.136 

B. 0.043 

C. 0.164 

D. 0.056 

Solution