Chapter 5. Decimals. Introduction to Decimals. 5.1. Decimal Notation. Like fractional notation, decimal notation is used to denote a part of a whole. Numbers written in decimal notation are called decimal numbers , or simply decimals . The decimal 16.734 has three parts. 16.743.
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Like fractional notation, decimal notation is used to denote a part of a whole. Numbers written in decimal notation are called decimal numbers, or simply decimals. The decimal 16.734 has three parts.
Whole number part
The position of each digit in a number determines its place value.
1 6 7 3 4
Notice that the value of each place is
of the value of the place to its left.
The digit 3 is in the hundredths place, so
its value is 3 hundredths or .
Step 1: Write the whole number part in words.
Step 2: Write “and” for the decimal point.
Step 3: Write the decimal part in words as though it were a whole number, followed by the place value of the last digit.
whole number part
Write the decimal 143.056 in words.
one hundred forty-three
Writing Decimals in Standard Form
Write one hundred six and five hundredths in standard form.
one hundred six and five hundredths
5 must be in the
When writing a decimal from words to decimal notation, make sure the last digit is in the correct place by inserting 0s after the decimal point if necessary.
three and fifty-four thousandths is 3.054
Once you master writing and reading decimals correctly, then you write a decimal as a fraction using the fractions associated with the words you use when you read it.
is read “nine tenths” and written as a fraction as
0.21 is read as
and written as a fraction as
0.011 is read as
and written as a fraction as
3 decimal places
2 decimal places
Notice that the number of decimal places in a decimal number is the same as the number of zeros in the denominator of the equivalent fraction. We can use this fact to write decimals as fractions.
One way to compare decimals is to compare their graphs on a number line. Recall that for any two numbers on a number line, the number to the left is smaller and the number to the right is larger. To compare 0.3 and 0.7 look at their graphs.
0.3 < 0.7 or 0.7 > 0.3
Comparing decimals by comparing their graphs on a number line can be time consuming, so we compare the size of decimals by comparing digits in corresponding places.
Compare digits in the same places from left to right. When two digits are not equal, the number with the larger digit is the larger decimal. If necessary, insert 0s after the last digit to the right of the decimal point to continue comparing.
Compare hundredths place digits.
For any decimal, writing 0s after the last digit to the right of the decimal point does not change the value of the number.
8.5 = 8.50 = 8.500, and so on
When a whole number is written as a decimal, the decimal point is placed to the right of the ones digit.
15 = 15.0 = 15.00, and so on
We round the decimal part of a decimal number in nearly the same way as we round whole numbers. The only difference is that we drop digits to the right of the rounding place, instead of replacing these digits by 0s. For example,
63.782 rounded to the nearest hundredth is
Step 1: Locate the digit to the right of the given place value.
Step 2: If this digit is 5 or greater, add 1 to the digit in the given place value and drop all digits to the right. If this digit is less than 5, drop all digits to the right of the given place.
digit to the right
Round 326.4386 to the nearest tenth.
Locate the digit to the right of the tenths place.
Since the digit to the right is less than 5, drop it and all digits to its right.
326.4386 rounded to the nearest tenths is 326.4