=13-27 Dr. Mark Greenberg practices dentistry in Topeka, Kansas. Greenberg tries hard to schedule appointments so that patients do not have to wait beyond their appointment time. His October 20 schedule is shown in the following table.

Scheduled Appointment and Time Expected Time Needed Adams 9:30 a.m. 15 Brown 9:45 a.m. 20 Crawford 10:15 a.m. 15 Dannon 10:30 a.m. 10 Erving 10:45 a.m. 30 Fink 11:15 a.m. 15 Graham 11:30 a.m. 20 Hinkel 11:45 a.m. 15 Unfortunately, not every patient arrives exactly on schedule, and expected times to examine patients are just that—expected. Some examinations take longer than expected, and some take less time.

Greenberg’s experience dictates the following:

(a) 20% of the patients will be 20 minutes early.

(b) 10% of the patients will be 10 minutes early.

(c) 40% of the patients will be on time.

(d) 25% of the patients will be 10 minutes late.

(e) 5% of the patients will be 20 minutes late.

He further estimates that

(a) 15% of the time he will finish in 20% less time than expected.

(b) 50% of the time he will finish in the expected time.

(c) 25% of the time he will finish in 20% more time than expected.

(d) 10% of the time he will finish in 40% more time than expected.