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 

Solution