2.3 Rounding

The precision and reporting of measurements depends on the tools that are used and the purpose of the measurement. In this section, we will study the impact and the importance of rounding.

The world population is the total number of living humans on the Earth, currently estimated by the United States Census Bureau to be 6.95 billion as of July 1, 2011.That is not an exact value—people are being born (and dying) every second—but it does give you an indication of the world’s population.

In newspapers and elsewhere, numbers are often rounded so that people can get a rough idea of the size, without getting lost in details. You use rounding in your everyday life, such as rounding prices in a supermarket ($2.99 is about $3) or distances (18.2 miles is about 20 miles), or time (it took about 40 minutes to get there, as opposed to 38.2 minutes).

Using approximate values is useful if you want to get a rough idea of an answer before you get out scratch paper or a calculator. This estimation acts as a check on your calculation and may help you to catch any errors you may have made—maybe you pressed a wrong key or reversed numbers.

In this section, you are going to look at rounding, and in the next section we will use estimation to solve problems.


U.S. Census Bureau, “World POPClock Projection.” Available online at http://www.census.gov/ population/ popclockworld.html [Tip: hold Ctrl and click a link to open it in a new tab. (Hide tip)] (accessed September 24, 2012).

2.2.5 Decimals in Daily Life

2.3.1 How Far is It?