**Decimal Fractions **(pg.13)

▪ Rule: All whole numbers are to the left of the

decimal; all decimal fractions are to the right

of the decimal point.

▪ To read a decimal fraction, read the number

to the right of the decimal and use the name

that applies to the “place value” of the last

figure.

▪ Decimal fractions read with a ths on the end.

▪ To read a whole number and a fraction, the

decimal point reads as an **and**.

▪ 0.3 = three tenths

▪ 0.5 = five tenths

▪ 1.3 = one and three tenths

▪ 1.5 = one and five tenths

▪ 0.12 = twelve hundreths

**Add, Subtract, Divide Decimals**

▪ 1.24 + 2.14 = 3.38

▪ 1.50 ÷ 2 = 0.75

▪ 2.650 ÷ 4 = 0.6625

**Round Decimals to nearest
10,100, Whole Numbers**

▪ Calculate one decimal place beyond the

desired place.

▪ If the final digit is 4 or less, make no

adjustment.

▪ If the final digit is 5 or more increase the

prior digit by one.

▪ Drop the final digit.

▪ Examples:

• 0.75 = 0.8 0.67 = 0.7 0.125 = 0.13 0.4 =

0.4

• 0.64 = 0.6 0.164 = 0.16 0.6 = 1

**Medication Alert!**

▪ **Do not** round medication dosages to

the nearest whole number. This could

result in a medication overdosage.

▪ **Rule**: Always round your answers to

the nearest measurable dose after you

verify that the dose is correct for that

patient.

**Ratio and Proportion**

▪ Ratio: Composed of two numbers which

are somehow related to each other. In

dosage problems, ratio is used to

represent the weight of a drug in a

certain volume of solution or package.

▪ Example:

• 1 ml: 100mg (ml contains 100mg of the drug)

• 1 tablet : 50 mg (1 tablet contains 50 mg of the

drug)

**Ratio & Proportion**

▪ Proportion: Consists of two ratios separated by an

equal sign which indicates that the two ratios are

equal.

▪ Example:

• 1 : 50 = 2 : 100

• 1 ml : 50 mg = 2 ml : 100 mg

• If 1 ml contains 50 mg then 2 ml contains 100mg

• The numbers on the end are called extremes

• The numbers in the middle are called means

▪ Example:

• 1 : 50 = 2 : 100, 1 : 50 = 2 : 100

• 1 times 100 = 100

• 50 times 2 = 100

▪ Ratio and proportion is used in dosage

calculations when only one ratio is known or

complete, and the other ratio is incomplete.

▪ Example: The doctor orders Lasix® 40 mg po stat.

What you have available is Lasix® 20 mg per tablet.

▪ Set up the problem:

• What you have Lasix 20 mg per 1 tablet

• What you want Lasix 40 mg per x tablet

• 20 mg : 1 tab = 40 mg : x tab

20 x = 1 ( 40 )

20 x = 40

x = 40/20

x = 2 tabs

**Ratio & Proportion Pointers**

* Set your problem up the same way each time. * Write what you have (or the known ratio) first this comes from the drug label. * Write what you want second (or the dosage ordered). * Make the x that you are solving for last. * You must write the ratio in the same |

sequence of measurement units or the

answer will be wrong.

**Example: mg : ml = mg : ml**

▪ Example: The doctor ordered 0.4 mg of

Atropine. The drugs label reads

1000mcg in 2 ml.

• __What you have__ 1000mcg per 2 ml

• __What you want__ 0.4 mg per ml

• To calculate the correct answer you must

first convert all measurement units to be

the same.

STEP 1

Convert 0.4 mg to 400 mcg

1 mg : 1000 mcg = 0.4 mg : x mcg

1x = 1000(0.4)

1x = 400

x = 400/1

x = 400mcg

STEP 2

**Solving the Problem**

__What you have__ 1000 mcg per 2 ml

__What you want__ 400 mcg per x ml (this is the

0.4 mg we converted to mcg in step#1)

1000 mcg : 2 ml = 400 mcg : x ml

1000x = 2(400)

1000x = 800

x = 800/1000

x = 0.8 ml

ALWAYS write a zero in front of the decimal point to prevent errors *

**Sample Problems**

▪ 25 mg = x g

▪ 0.3 mg = x g

▪ 2.8 L = x ml

▪ 1000 mg : 1 mg = 150 mg : x mg

▪ 200 mg : 5 ml = 300 mg : x ml

▪ 175 mcg : 1 tab = 350 mcg : x tab

▪ Ordered : Vistaril 60 mg

▪ Available : Vistaril 100mg/2ml

▪ Ordered : Heparin 2000u

▪ Available : Heparin 6000u/ml

▪ 20 mg is equal to how many gr?

60 mg : 1 gr = 20 mg : x gr

60 x = 20/60 = (1/3)

x = 0.333

▪ 1/4 tsp equals how many milliliters?

1 tsp : 5 ml = 1/4 tsp : x

1x = 5/4

x = 1.25

▪ 0.04 g = ____μg

1 g : 1000mg = 0.04 g : x mg

x = 40 mg

1 mg : 1000 μg = 40 mg : x μg

x = 40,000

▪ gr 1/6 = ____mg

1 gr : 60 mg = 1/6 : x mg

x = 60/6

x = 10 mg

**Questions?**