PART III: M ETHODS OF C ALCULATION
C HAPTER 5: L INEAR R ATIO AND P ROPORTION
Castillo: Calculating Drug Dosages: A Patient -Safe Approach to Nursing
and Math 2nd Edition
MULTIPLE CHOICE
1. The physician orders 2.5 mg of a medication IV dail y. The pharmacy
sends a 5 m L vial of the medication labeled 1.25 mg per mL. Which of the
following will the nurse use to set up the known ratio in a dosage
calculation?
A. 2.5 mg : 1 mg
B. 2.5 mg : 5 m L
C. 2.5 mg : 1.25 mg
D. 1.25 mg : 1 mL
ANS: D
Feedback
The known ratio is found on the label of the vial supplied by the
pharmacy: 1.25 mg per mL, or 1.25 mg : 1 mL.
2. The patient is to receive 7.5 mg of a medication PO dail y. The pharmacy
sends a bottle of scored tabl ets with the dosage strength of 15 mg each.
, The nurse sets up a ratio to solve a calculation for this ordered dose. In
addition to x tablet(s), what other number will the nurse use for the
unknown ratio?
A. 7.5 mg
B. 15 mg
C. 1 tablet
D. 2 tablets
ANS: A
Feedback
The unknown ratio includes the medication order and the unknown (in
this problem, x tablet). The order is 7.5 mg, so the unknown ratio is 7.5
mg : x tablet.
3. The medication administration record (MAR) includes an order for
gl ycopyrrolate oral solution 2 mg twice dail y PO. The medication drawer
contains gl ycopyrrolate oral solution labeled 1 mg/5 mL. Which of the
following is the correct setup for the drug dosage calculation?
A. 2 mg : 2 :: 1 mg : x
B. 2 mg : x mL :: 5 mL : 1 mg
C. 1 mg : 5 mL :: 2 mg : x mL
D. 5 mL : 1 mg :: 2 mg : x mL
ANS: C
Feedback
, The known ratio is from the available medication label (1 mg/5 mL)
and the unknown ratio includes the medication order and the unknown
(2 mg : x mL).
4. The nurse has a vial of furosemide labeled 10 mg/m L. The physician
orders furosemide 40 mg IVP now. Which proportion is correct to solve
for the ordered amount?
A. 10 mg : 40 mg :: x mL : 1 mL
B. 10 mg : x mL :: 40 mg : 1 mL
C. 10 mg : m L :: 40 mg : x mL
D. 10 mg : 1 mL :: 40 mg : x mL
ANS: D
Feedback
The known ratio is from the available medication label (10 mg/mL) and
the unknown ratio includes the medication order and the unknown “x”
(40 mg : x mL).
5. Which of the following proportions is correctl y set up so that the units
match?
A. 500 mg : x tab :: 250 mg : 1 tab
B. 1 g : 1,000 mg :: 500 mg : x mL
C. 1,000 mcg : 0.1 m L :: x mL : 1,500 mcg
D. 4 mg : 1 capsule :: x capsule : 12 mg
ANS: A
, Feedback
When checking the units of measurement, both ratios must contain the
same two units in the same order. Onl y the first ratio has the same two
units (mg and tab) in the same order in each ratio (mg : tab, mg : tab).
6. The nurse is preparing to administer digoxin injection to a patient. The
order is for 100 mcg IV this morning. A vial of digoxin Injection is in the
patient’s medication drawer that has the following dosage strengths on the
label:
500 mcg (0.5 mg) in 2 mL
(250 mcg [0.25 mg] per mL)
Select the ratio that does not require the nurse to do a conversion to solve
for the ordered dose.
A. 500 mcg : 0.5 mL
B. 0.5 mg : 2 m L
C. 250 mcg : 1 m L
D. 0.25 mg : 1 mL
ANS: C
Feedback
Because the order is in mcg, the nurse can use 250 mcg per 1 mL to
solve for the number of mL to administer with no conversion needed.
The choices with mg (2 and 4) require a conversion from mcg to mg
before calculating the dose. Choi ce A (500 mcg in 0.5 m L) is not a
dosage strength written on this label.
C HAPTER 5: L INEAR R ATIO AND P ROPORTION
Castillo: Calculating Drug Dosages: A Patient -Safe Approach to Nursing
and Math 2nd Edition
MULTIPLE CHOICE
1. The physician orders 2.5 mg of a medication IV dail y. The pharmacy
sends a 5 m L vial of the medication labeled 1.25 mg per mL. Which of the
following will the nurse use to set up the known ratio in a dosage
calculation?
A. 2.5 mg : 1 mg
B. 2.5 mg : 5 m L
C. 2.5 mg : 1.25 mg
D. 1.25 mg : 1 mL
ANS: D
Feedback
The known ratio is found on the label of the vial supplied by the
pharmacy: 1.25 mg per mL, or 1.25 mg : 1 mL.
2. The patient is to receive 7.5 mg of a medication PO dail y. The pharmacy
sends a bottle of scored tabl ets with the dosage strength of 15 mg each.
, The nurse sets up a ratio to solve a calculation for this ordered dose. In
addition to x tablet(s), what other number will the nurse use for the
unknown ratio?
A. 7.5 mg
B. 15 mg
C. 1 tablet
D. 2 tablets
ANS: A
Feedback
The unknown ratio includes the medication order and the unknown (in
this problem, x tablet). The order is 7.5 mg, so the unknown ratio is 7.5
mg : x tablet.
3. The medication administration record (MAR) includes an order for
gl ycopyrrolate oral solution 2 mg twice dail y PO. The medication drawer
contains gl ycopyrrolate oral solution labeled 1 mg/5 mL. Which of the
following is the correct setup for the drug dosage calculation?
A. 2 mg : 2 :: 1 mg : x
B. 2 mg : x mL :: 5 mL : 1 mg
C. 1 mg : 5 mL :: 2 mg : x mL
D. 5 mL : 1 mg :: 2 mg : x mL
ANS: C
Feedback
, The known ratio is from the available medication label (1 mg/5 mL)
and the unknown ratio includes the medication order and the unknown
(2 mg : x mL).
4. The nurse has a vial of furosemide labeled 10 mg/m L. The physician
orders furosemide 40 mg IVP now. Which proportion is correct to solve
for the ordered amount?
A. 10 mg : 40 mg :: x mL : 1 mL
B. 10 mg : x mL :: 40 mg : 1 mL
C. 10 mg : m L :: 40 mg : x mL
D. 10 mg : 1 mL :: 40 mg : x mL
ANS: D
Feedback
The known ratio is from the available medication label (10 mg/mL) and
the unknown ratio includes the medication order and the unknown “x”
(40 mg : x mL).
5. Which of the following proportions is correctl y set up so that the units
match?
A. 500 mg : x tab :: 250 mg : 1 tab
B. 1 g : 1,000 mg :: 500 mg : x mL
C. 1,000 mcg : 0.1 m L :: x mL : 1,500 mcg
D. 4 mg : 1 capsule :: x capsule : 12 mg
ANS: A
, Feedback
When checking the units of measurement, both ratios must contain the
same two units in the same order. Onl y the first ratio has the same two
units (mg and tab) in the same order in each ratio (mg : tab, mg : tab).
6. The nurse is preparing to administer digoxin injection to a patient. The
order is for 100 mcg IV this morning. A vial of digoxin Injection is in the
patient’s medication drawer that has the following dosage strengths on the
label:
500 mcg (0.5 mg) in 2 mL
(250 mcg [0.25 mg] per mL)
Select the ratio that does not require the nurse to do a conversion to solve
for the ordered dose.
A. 500 mcg : 0.5 mL
B. 0.5 mg : 2 m L
C. 250 mcg : 1 m L
D. 0.25 mg : 1 mL
ANS: C
Feedback
Because the order is in mcg, the nurse can use 250 mcg per 1 mL to
solve for the number of mL to administer with no conversion needed.
The choices with mg (2 and 4) require a conversion from mcg to mg
before calculating the dose. Choi ce A (500 mcg in 0.5 m L) is not a
dosage strength written on this label.
