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 effective period of the tranquilizer for each patient (in hours) was as follows: 2.7; 2.8; 3.0; 2.3; 2.3; 2.2; 2.8; 2.1; and 2.4.

a. i. x - = __________ ii. sx = __________ iii. n = __________ iv. n – 1 = __________

b. Define the random variable X in words.

c. Define the random variable X - in words.

d. Which distribution should you use for this problem? Explain your choice.

e. Construct a 95% confidence interval for the population mean length of time.

i. State the confidence interval.

ii. Sketch the graph.

f. What does it mean to be “95% confident” in this problem?