Naming Decimals

Naming Decimals

You probably already know quite a bit about decimals based on your experience with money. Suppose you buy a sandwich and a bottle of water for lunch. If the sandwich costs \(\text{\$3.45}\), the bottle of water costs \(\text{\$1.25}\), and the total sales tax is \(\text{\$0.33}\), what is the total cost of your lunch?

Naming Decimals

The total is \(\text{\$5.03}.\) Suppose you pay with a \(\text{\$5}\) bill and \(3\) pennies. Should you wait for change? No, \(\text{\$5}\) and \(3\) pennies is the same as \(\text{\$5.03}.\)

Because \(\text{100 pennies}=\text{\$1},\) each penny is worth \(\frac{1}{100}\) of a dollar. We write the value of one penny as \(\$0.01,\) since \(0.01=\frac{1}{100}.\)

Writing a number with a decimal is known as decimal notation. It is a way of showing parts of a whole when the whole is a power of ten. In other words, decimals are another way of writing fractions whose denominators are powers of ten. Just as the counting numbers are based on powers of ten, decimals are based on powers of ten. The table below shows the counting numbers.

Counting numberName
\(1\)One
\(10=10\)Ten
\(10·10=100\)One hundred
\(10·10·10=1000\)One thousand
\(10·10·10·10=10,000\)Ten thousand

How are decimals related to fractions? The table below shows the relation.

DecimalFractionName
\(0.1\)\(\frac{1}{10}\)One tenth
\(0.01\)\(\frac{1}{100}\)One hundredth
\(0.001\)\(\frac{1}{1,000}\)One thousandth
\(0.0001\)\(\frac{1}{10,000}\)One ten-thousandth

When we name a whole number, the name corresponds to the place value based on the powers of ten. In Mathematics 101, we learned to read \(10,000\) as ten thousand. Likewise, the names of the decimal places correspond to their fraction values. Notice how the place value names in the figure below relate to the names of the fractions from the table above

Naming Decimals

This chart illustrates place values to the left and right of the decimal point.

Notice two important facts shown in the figure above.

  • The “th” at the end of the name means the number is a fraction. “One thousand” is a number larger than one, but “one thousandth” is a number smaller than one.
  • The tenths place is the first place to the right of the decimal, but the tens place is two places to the left of the decimal.

Remember that \(\text{\$5}.03\) lunch? We read \(\text{\$5.03}\) as five dollars and three cents. Naming decimals (those that don’t represent money) is done in a similar way. We read the number \(5.03\) as five and three hundredths.

We sometimes need to translate a number written in decimal notation into words. As shown in the figure below, we write the amount on a check in both words and numbers.

Naming Decimals

When we write a check, we write the amount as a decimal number as well as in words. The bank looks at the check to make sure both numbers match. This helps prevent errors.

Let’s try naming a decimal, such as 15.68. 
We start by naming the number to the left of the decimal.fifteen______
We use the word “and” to indicate the decimal point.fifteen and_____
Then we name the number to the right of the decimal point as if it were a whole number.fifteen and sixty-eight_____
Last, name the decimal place of the last digit.fifteen and sixty-eight hundredths

The number \(15.68\) is read fifteen and sixty-eight hundredths.

How to Name a decimal number.

  • Name the number to the left of the decimal point.
  • Write “and” for the decimal point.
  • Name the “number” part to the right of the decimal point as if it were a whole number.
  • Name the decimal place of the last digit.

Example

Name each decimal:

  1. \(\phantom{\rule{0.2em}{0ex}}4.3\)
  2. \(\phantom{\rule{0.2em}{0ex}}2.45\)
  3. \(\phantom{\rule{0.2em}{0ex}}0.009\)
  4. \(\phantom{\rule{0.2em}{0ex}}-15.571.\)

Solution

  
 4.3
Name the number to the left of the decimal point.four_____
Write “and” for the decimal point.four and_____
Name the number to the right of the decimal point as if it were a whole number.four and three_____
Name the decimal place of the last digit.four and three tenths
  
 2.45
Name the number to the left of the decimal point.two_____
Write “and” for the decimal point.two and_____
Name the number to the right of the decimal point as if it were a whole number.two and forty-five_____
Name the decimal place of the last digit.two and forty-five hundredths
  
 0.009
Name the number to the left of the decimal point.Zero is the number to the left of the decimal; it is not included in the name.
Name the number to the right of the decimal point as if it were a whole number.nine_____
Name the decimal place of the last digit.nine thousandths
  
 \(-15.571\)
Name the number to the left of the decimal point.negative fifteen
Write “and” for the decimal point.negative fifteen and_____
Name the number to the right of the decimal point as if it were a whole number.negative fifteen and five hundred seventy-one_____
Name the decimal place of the last digit.negative fifteen and five hundred seventy-one thousandths

Optional Video: Introduction to Decimal Notation

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This is a lesson from the tutorial, Introducing Decimals and you are encouraged to log in or register, so that you can track your progress.

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