Copyright © 2015 Cengage Learning® Chapter 1 Relative Value, Addition and Subtraction of Decimals

Copyright © 2015 Cengage Learning®

Chapter 1

Relative Value, Addition andSubtraction of Decimals

Copyright © 2015 Cengage Learning®Copyright © 2015 Cengage Learning®

Decimals

• Health care professionals deal with decimal fraction dosages on a daily basis.

• Helpful hint:– Consider United States (U.S.) monetary system of

dollars and cents.

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0,000,000.000

Note that the numbers after the decimal end in “th.”

Decimal Place Value

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Number of Decimal Places

• Consider only three decimal places after decimal point.– Drug dosages measured as decimal fractions do not

contain more than three digits.

– For example, 0.025

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Relative Value of Decimals

• Whole number– Number to left of decimal point

• Greater the whole number, greater the value– For example, 5.078 greater than 4.997

(continues)

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Relative Value of Decimals (cont’d)

• Fraction determines relative value if:– Equal whole numbers

– No whole numbers

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Greatest Value

• Which of the following numbers hasthe greatest value?a. 3.3

b. 2.7

c. 4.5

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Fractional Side: Another Look

• 0.125– Zero represents whole number.

– One represents tenths.

– Two represents hundredths.

– Five represents thousandths.

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Zeros

• If decimal fraction not preceded by whole number, use zero in front of decimal point.– Emphasizes that number is a fraction

– Prevents overlooking decimal point

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Greatest Value: Tenths

• Fraction with greater numberrepresenting tenths has greater value.

• Which of the following decimal fractionshas the greatest value?a. 0.178

b. 0.521

c. 0.276

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Greatest Value: Hundredths

• When the tenths digits are identical, the fraction with greater number representing hundredths has the greater value.

Example:

0.23

0.28 This one is the larger.

(continues)

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Greatest Value: Hundredths (cont’d)

• Which of the following decimal fractionshas the greatest value?a. 2.25b. 2.22c. 2.28

• Here is one that is tricky:a. 0.4 This one is the largest (0.4 is the same as 0.40).b. 0.36 You may always add zeros at the end to make the decimals

the same length.

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Adding and Subtracting

• Use calculator for most addition and subtraction of decimal fractions.Practice using until proficient.

• When manually adding or subtracting decimal fractions, first line up the decimal points, then add or subtract from left to right.

(continues)

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Adding and Subtracting (cont’d)

• Line up decimal points when writing down the number:

0.25

0.27

0.52

0.82

– 0.63

0.19

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0.123

0.7

0.823

Practice Addition

2.45

3.47

5.92

0.078

1.142

1.220

Remember you may add zeros at the end of the number to make them equal length. 0.7 would then be 0.700.

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1.25

– 1.125

0.125

Practice Subtraction

0.07

– 0.035

0.035

7.33

– 4.03

3.3

Add a 0 after the 7 to make the numbers the same length for subtraction. 0.07 becomes 0.070.

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Note About Decimals

• Extra zeros on the end of decimal fractionscan be a source of error in drug dosages, and are routinely eliminated. So when you get your final answer, be sure unnecessary zeros are removed.

Examples:

0.012000 = 0.012

4.200 = 4.2

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Dosage Calculations

• Prescription for 0.4 mg

• Have 0.1 mg tablets on hand

• How many tablets should be administered?a. 1 tablet

b. Less than 1 tablet

c. More than 1 tablet

(continues)

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Dosage Calculations (cont’d)






(continues)

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Dosage Calculations (cont’d)






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Practice, Practice, Practice

• More practice means:– Increased proficiency and accuracy

– Decreased risk of errors

– Increased comfort level with calculations

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Documents

Copyright © 2015 Cengage Learning® Chapter 1 Relative Value, Addition and Subtraction of Decimals