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# Chapter 18. Hold on a Second: Time Math

In This Chapter

• Recognizing time units

• Identifying different methods of noting time

• Converting time in traditional, fractional, and decimal form

• Performing basic time addition, subtraction, multiplication, and division

Time is an essential and undeniable part of the human experience. That's a lofty statement in a book about technical mathematics. But it's true — reckoning time is a vital component of almost every civilization.

Time is easy to read, report, measure, and calculate. In this chapter, you see how to denote time in both common and uncommon ways. You convert time into traditional, fractional, and decimal forms and perform some time math.

### Note

Many societies are run by time: They're deadline-driven and have a very low tolerance for tardiness. But at least one place has no concept of time. The Pirahã people on the Mai ci river in the Amazon rainforest speak by humming and whistling; they have no more than eight consonants and three vowels and have no numbers and no time.

# Dividing Time into Hours, Minutes, and Seconds

Time is the most precisely measured quantity on earth. Atomic clocks are accurate to 10−9 seconds (one billionth of a second) per day, and accurate time is essential for maintaining the frequency of television broadcasts and operating the GPS system.

Time is important in both business and personal activity in the following ways:

• Time is a measure of progress or capacity. For example, you say "How much did you get done on the project ...

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