You have purchased a smart phone that has a battery system advertised as allowing 22 hours of talk time before it requires recharging. A friend of yours advises you that it is a good phone, but the 22 hours of talk time is a highly theoretical number, based on ideal conditions concerning the placement of the phone towers around you as you talk, the exact number of calls you initiated while talking, and the state of the battery when you last charged the phone. As a result of these issues, your friend warns you that you can generally only expect 20 hours of talk time from the battery system.

a. The issue of 22 hours of talk time is best described as what?

b. The issue concerning the actual placement of the phone towers around you as you talk is best described by what concept?

c. You only talk 10 hours a day on your phone, and you always recharge it over- night. If you just consider talk time, how efficient is your use of this phone's battery system?