Solution We start by guessing that the typical life span is about 70 years. The only other estimate we must make in this
example is the average number of breaths that a person takes in 1 min. This number varies, depending on whether
the person is exercising, sleeping, angry, serene, and so forth. To the nearest order of magnitude, we shall choose 10 breaths per minute as our estimate of the average. (This iscertainly closer to the true value than 1 breath perminute or 100 breaths per minute.) The number of minutes in a year is approximately