Chapter 1 Relative Value Addition and Subtraction of

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

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. Copyright © 2015 Copyright Cengage©Learning® 2015 Cengage Learning® 1 -2

Thousandths Hundredths Tens Ones or units Decimal Tenths Hundreds Thousands Ten-thousands Hundred-thousands Millions Decimal Place Value 0, 000 Note that the numbers after the decimal end in “th. ” Copyright © 2015 Copyright Cengage©Learning® 2015 Cengage Learning® 1 -3

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 Copyright © 2015 Copyright Cengage©Learning® 2015 Cengage Learning® 1 -4

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) Copyright © 2015 Copyright Cengage©Learning® 2015 Cengage Learning® 1 -5

Relative Value of Decimals (cont’d) • Fraction determines relative value if: – Equal whole

Greatest Value • Which of the following numbers has the greatest value? a. 3.

Fractional Side: Another Look • 0. 125 – – Zero represents whole number. One represents tenths. Two represents hundredths. Five represents thousandths. Copyright © 2015 Copyright Cengage©Learning® 2015 Cengage Learning® 1 -8

$Zeros • If decimal fraction not preceded by whole number, use zero in front$

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 Copyright © 2015 Copyright Cengage©Learning® 2015 Cengage Learning® 1 -9

Greatest Value: Tenths • Fraction with greater number representing tenths has greater value. • Which of the following decimal fractions has the greatest value? a. 0. 178 b. 0. 521 c. 0. 276 Copyright © 2015 Copyright Cengage©Learning® 2015 Cengage Learning® 1 -10

$Greatest Value: Hundredths • When the tenths digits are identical, the fraction with greater$

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) Copyright © 2015 Copyright Cengage©Learning® 2015 Cengage Learning® 1 -11

$Greatest Value: Hundredths (cont’d) • Which of the following decimal fractions has the greatest$

Greatest Value: Hundredths (cont’d) • Which of the following decimal fractions has the greatest value? a. 2. 25 b. 2. 22 c. 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. Copyright © 2015 Copyright Cengage©Learning® 2015 Cengage Learning® 1 -12

$Adding and Subtracting • Use calculator for most addition and subtraction of decimal fractions.$

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) Copyright © 2015 Copyright Cengage©Learning® 2015 Cengage Learning® 1 -13

Adding and Subtracting (cont’d) • Line up decimal points when writing down the number:

Practice Addition Remember you may add zeros at the end of the number to

Practice Subtraction Add a 0 after the 7 to make the numbers the same

$Note About Decimals • Extra zeros on the end of decimal fractions can be$

Note About Decimals • Extra zeros on the end of decimal fractions can 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 Copyright © 2015 Copyright Cengage©Learning® 2015 Cengage Learning® 1 -17

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) Copyright © 2015 Copyright Cengage©Learning® 2015 Cengage Learning® 1 -18

Dosage Calculations (cont’d) • Prescription for 0. 125 mg • Have 0. 25 mg tablets on hand • How many tablets should be administered? a. 1 tablet b. Less than 1 tablet c. More than 1 tablet (continues) Copyright © 2015 Copyright Cengage©Learning® 2015 Cengage Learning® 1 -19

Dosage Calculations (cont’d) • Prescription for 0. 5 mg • Have 0. 5 mg tablets on hand • How many tablets should be administered? a. 1 tablet b. Less than 1 tablet c. More than 1 tablet Copyright © 2015 Copyright Cengage©Learning® 2015 Cengage Learning® 1 -20

Practice, Practice • More practice means: – Increased proficiency and accuracy – Decreased risk of errors – Increased comfort level with calculations Copyright © 2015 Copyright Cengage©Learning® 2015 Cengage Learning® 1 -21