Math Calculation Practice Questions

Remember, for all math calculations:
v
Label
each part of your calculation to stay on track
v
If you
are working with different units of measurements, you need to
convert
to equivalent measures
v
Read the
question carefully. Is it asking for a single dose, total dose in 24 hours,
dose based on weight, or safe range of a dose?
v
Use correct interpretation of
abbreviations – examples:
1.
You have an order to give Penicillin 150,000U (I.M.). You have a vial
of Penicillin containing 3,000,000Units in 10ml. How many ml will you give?
0.5ml Three ways to set up problem: a. X ml :150,000Units = 10 ml : 3,000,000Units
b.
3,000,000 U = 150,000
U
c.
150,000 U
x 10 ml
Dose Desired x
Volume 2. The doctor orders Demerol 25mg. (I.M.) q4h prn. You have Demerol 100mg. in 2ml. How many ml will you give? 0.5ml a. X ml
: 25mg = 2ml : 100mg b.
100 mg = 25
mg c.
25mg x 2 ml

3.
Your patient is to receive Digoxin 0.125
mg. On hand you have Digoxin 500mcg in 2 cc’s.
How many cc’s will you give?
0.5 cc First convert mcg to mg.
500mcg = 0.5mg Then set up problem as above.

4.
The drug order reads ASA gr.X
q4h prn. for
headache. You have ASA 325 mg tablets. How many tablets will you give?
2 tablets First convert grains to mg.
60 mg = 1gr. therefore
10grains = 600mg. X tab : 600mg = 1
tab : 325mg After setting up and solving problem the result
will be 1.8 tablets. You will give two tablets – remember that converting from
METRIC SYSTEM TO AN APOTHECARY SYSTEM FREQUENTLY RESULTS IN
EQUIVALENTS

5.
The doctor’s order reads: Phenobarbital gr. ss
(1/2) q6h. You have
Phenobarbital 15 mg tablets. How many tablets will you give?
2 tablets First convert grains to mg.
1/2gr
x 60 = 30mg

6.
In question #5, how many tablets will you give in 24 hours?
8 tablets Q6h = 4 times a day spaced at 6 hour intervals
(24 hours =
4 doses)^{
}6 hour

7. The doctor orders Atropine gr. 1/200 stat. You have a vial that reads:
Atropine gr. 1/150 in 2cc. How many ml’s
will you give? 1.5ml. (Tests ability to multiply and divide fractions) 
8. Your patient is to receive Atropine 0.3 mg. You have Atropine 1/150 gr.
in 1 ml. How many ml’s will you give?
0.75ml First convert grains to mg. 60 x 1/150 = 0.4 mg 1/150 gr = 0.4 mg

9.
The order reads: Valium 15 mg p.o. T.I.D.
The label reads: Valium gr. ½. How many tablets would you give in a 24hour
period? 1 ½ tablets First convert grains to mg ½ x 60 = 30 mg. You will give ½ tablet three times in 24 hours.
½ x 3 = 1 ½

10.
The doctor orders Streptomycin 400mg. The vial label reads Streptomycin
1 Gm in 2.5 ml. How many ml will you give?
1 cc First convert Gm to mg. 1Gm = 1000mg.

11. You are to give 240 cc of osmolyte through a
feeding tube over a three hour period. The drop factor for the solution set is
15. How many drops per minute will you give?
20gtts/minute Formula
= volume in one hour x gtt
factor First calculate how many ml in one hour = 80ml 80 ml x 15(gtt factor)
=
20 gtts/minute

12. The doctor orders Klonopin 1 mg daily for a child who weighs 36 pounds. Calculate the safe range for this medication based on a safe range of 0.01 – 0.05mg/kg/day. First calculate the
child's weight in kilograms (kg). Divide 36 lb by 2.2 kg = 16.36 kg Multiply
the child’s weight in kg by the lowest and highest safe dose. The safe range is
0.01mg/16.36kg/day ( 0.01 x 16.36 = 0.16mg)
to 0.05mg/16.36kg/day (0.05 x 16.36 = 0.82mg).

13. Will you give the child the dose ordered? No No because 1.00 mg
exceeds the highest safe dose of 0.82 mg. 
Visualize the difference between milligrams, grains, and Grams
Weights
Metric 
Apothecary 
Metric 

1 milligram (1 mg ) 
1/60 grain (gr) 
0.001 Gram (0.001Gm) 

60 milligrams (60 mg) 
1 grain (1 gr) 
0.06 Gram (0.06Gm) 

1000 mg 
15 gr 
1 Gm 

1000 micrograms (mcg) = 
1 mg 
0.001 Gm 

Grams to grains = multiply by 15
Grains to Grams = divide by 15
Grains to milligrams = multiply by 60
milligrams to grains = divide by 60
Grams to milligrams = move decimal point three places to the right
milligrams to Grams = move decimal point three places to left
micrograms to milligrams = move decimal point three places to left
Volumes
1.0 milliliter (ml or cc) 
15 minims (m) 
15 drops (gtts) 

5.0 ml (cc) 
1 dram 
1 tsp. 

30 ml (cc) 
1 ounce (oz) 
8 tsp. = 2 T 

500 ml (cc) 
1 pint (pt.) 
2 cups 

1000 ml (cc) = 1 liter (L) 
1 quart (qt) 
4 cups 

Weight 2.2 pounds ( lb ) = 1 kilogram (kg)
kg to pounds = kg x 2.2 lb to kg = lb ÷ 2.2