1. An airline wants to evaluate the depth perception of its pilots over the age of fifty. A random sample of n = 17 airline pilots over the age of fifty are asked to judge the distance between two markers placed 20 feet apart at the opposite end of the laboratory. The population standard deviation is 1.4. The sample data listed here are the pilots' error (recorded in feet) in judging the distance. 

1.99    2.58    2.91    1.53    2.64    2.67    2.24    2.25    2.25

2.11      2.28    2.07    2.16    2.50    2.86    2.43    2.2

a) What is the sample mean? (Use either SPSS or a calculator.)

b) Is there evidence that the mean error in depth perception for the company's pilots over the age of fifty is greater than 2.1? Use α = 0.05.

c) What is the 90% confidence interval for the mean error in depth perception? (Remember, the form of the confidence interval when the population standard deviation is known is: ()