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 Dependent Variable

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# Fractions

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 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

▪ 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
▪ 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

Do not round medication dosages to
the nearest whole number. This could
result in a medication overdosage.
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

Example: mg : ml = mg : ml

▪ Example: The doctor ordered 0.4 mg of
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?