A computer lab at a small college has 25 computers.

Twice during the day a full scan for viruses is performed on each computer. Because of differences in the configuration of the computers, the times required to complete the scan are different for each machine.

Records for the scans are kept and indicate that the time (in seconds) required to perform the scan for each machine is as shown here.

Time in Seconds to Complete Scan 1,500 1,347 1,552 1,453 1,371 1,362 1,447 1,362 1,216 1,378 1,647 1,093 1,350 1,834 1,480 1,522 1,410 1,446 1,291 1,601 1,365 1,575 1,134 1,532 1,534

a. What is the mean time required to scan all 25 computers?

b. Suppose a random sample of 5 computers is taken and the scan times for each are as follows: 1,534, 1,447, 1,371, 1,410, and 1,834. If these 5 randomly sampled computers are used to estimate the mean scan time for all 25 computers, what would the sampling error be?

c. What is the range of possible sampling error if a random sample size of 7 computers is taken to estimate the mean scan time for all 25 machines?