When an approximate value for a measurement, or other number, is needed, rounding can be used. For example, a person might say that he or she owns 100 books when the actual number of books that person owns might be 98 or 104. Sometimes the process of giving an approximate number is also called rounding off.

Suppose a measurement of 15.42 inches needs to be rounded to the nearest inch. The first step is to ask this question: "Is 15.42 inches closer to 15 inches or to 16 inches?" Because 15.42 is closer to 15 inches, 15.42 rounds to 15. Similarly, a measurement of 15.62 inches would be rounded to 16.

But what about a measurement of 15.5 inches? This measurement is exactly halfway between 15 and 16 inches. There are two ways to solve this dilemma. The first way, which is the most often used, is to round up when the digit is 5. Thus 15.5 rounds to 16. But what about 15.55? This is not midway...