A pharmaceutical company makes tranquilizers. It is assumed that the distribution for the length of time they last is approximately normal. Researchers in a hospital used the drug on a random sample...

Extracted text: A pharmaceutical company makes tranquilizers. It is assumed that the distribution for the length of time they last is approximately normal. Researchers in a hospital used the drug on a random sample of nine patients. The effectiveness periods of the tranquilizer for each patient (in hours) were as follows: 2.7, 2.8, 3.0, 2.3, 2.3, 2.2, 2.8, 2.1and 2.4. If the error bound is 0.3556, then the level of confidence interval of the mean is: O 0.99 0.98 O None of the other options O 0.95