Dimensional Analysis
Calculating Dosages Safely
3rd Edition
• Author(s)Tracy Horntvedt
TEST BANK
1)
Reference: Ch. 1 — Whole Numbers — Types of Numbers
Stem: The provider orders amoxicillin 2 g PO now. The supply
on hand is 500 mg tablets. Using dimensional analysis, how
many tablets should the nurse administer?
Options:
A. 2 tablets
B. 3 tablets
C. 4 tablets
D. 5 tablets
,Correct answer: C. 4 tablets
Rationale — Correct (C):
Set up:
2 g×1000 mg1 g×1 tablet500 mg=2000 mg500 mg/tablet=4 tabl
ets.2\ \text{g} \times \dfrac{1000\ \text{mg}}{1\ \text{g}} \times
\dfrac{1\ \text{tablet}}{500\ \text{mg}} = \dfrac{2000\
\text{mg}}{500\ \text{mg/tablet}} = 4\
\text{tablets}.2 g×1 g1000 mg×500 mg1 tablet
=500 mg/tablet2000 mg=4 tablets. Units cancel (g → mg →
tablet). Whole-number conversions produce 2000 mg ÷ 500 mg
= 4. This dose is appropriate given the order and requires no
rounding.
Rationale — Incorrect:
A. (2 tablets) — Represents halving: 2000 mg ÷ 1000 mg (wrong
tablet strength), incorrect unit cancellation. Unsafe underdose.
B. (3 tablets) — Likely from 2000 ÷ 3 ≈ 667 mg assumption or
decimal truncation; indicates calculation error (non-integer
tablet assumption). Unsafe/incorrect.
D. (5 tablets) — Likely from 250 mg misread or addition error;
would give 2500 mg (overdose).
Teaching point: Convert units to the same base (g → mg) before
dividing by strength.
Citation: Horntvedt, T. (3rd ed.). Dimensional Analysis:
Calculating Dosages Safely. Ch. 1.
,2)
Reference: Ch. 1 — Whole Numbers — Adding Whole Numbers
Stem: A nurse is preparing a once-daily pill tray. Orders:
metformin 500 mg PO BID and simvastatin 20 mg PO qHS. The
pharmacy delivered metformin 500 mg tablets and simvastatin
20 mg tablets. For the 24-hour medication count, how many
total tablets will be placed in the tray? (Use whole-number
addition.)
Options:
A. 3 tablets
B. 4 tablets
C. 5 tablets
D. 6 tablets
Correct answer: B. 4 tablets
Rationale — Correct (B):
Metformin 500 mg BID = 2 tablets/day (500 mg each, two
doses). Simvastatin 20 mg qHS = 1 tablet/day. Total = 2 + 1 = 3
tablets — but check: BID means twice daily, and simvastatin
qHS is once nightly -> total 3. Wait—option mismatch; correct
calculation yields 3 tablets. (Correction: The correct answer is
A. 3 tablets.)
[Adjusted final answer below — correcting to follow
dimensional/addition logic]
Correct answer (revised): A. 3 tablets
, Rationale — Correct (A):
Addition: metformin = 2 tablets/day; simvastatin = 1 tablet/day;
total = 2 + 1 = 3 tablets. Units: tablets are like units — simple
whole-number addition. No conversion or rounding needed.
Rationale — Incorrect:
B. (4 tablets) — Overcounts one extra tablet; common error:
interpreting BID as three times.
C. (5 tablets) — Likely misreading of doses or thinking BID
applies to each med.
D. (6 tablets) — Doubling both meds erroneously; arithmetic
error.
Teaching point: Count like units (tablets) and add totals; clarify
dosing frequency abbreviations.
Citation: Horntvedt, T. (3rd ed.). Dimensional Analysis:
Calculating Dosages Safely. Ch. 1.
3)
Reference: Ch. 1 — Whole Numbers — Subtracting Whole
Numbers
Stem: The med cart contains 30 tablets of oxybutynin 5 mg.
After administering morning doses, 7 tablets remain to be given
throughout the day. A patient receives an additional dose of 1
tablet now. How many tablets remain in stock for the rest of the
day? (Use whole-number subtraction and show dimensional
logic: tablets → tablets.)
Calculating Dosages Safely
3rd Edition
• Author(s)Tracy Horntvedt
TEST BANK
1)
Reference: Ch. 1 — Whole Numbers — Types of Numbers
Stem: The provider orders amoxicillin 2 g PO now. The supply
on hand is 500 mg tablets. Using dimensional analysis, how
many tablets should the nurse administer?
Options:
A. 2 tablets
B. 3 tablets
C. 4 tablets
D. 5 tablets
,Correct answer: C. 4 tablets
Rationale — Correct (C):
Set up:
2 g×1000 mg1 g×1 tablet500 mg=2000 mg500 mg/tablet=4 tabl
ets.2\ \text{g} \times \dfrac{1000\ \text{mg}}{1\ \text{g}} \times
\dfrac{1\ \text{tablet}}{500\ \text{mg}} = \dfrac{2000\
\text{mg}}{500\ \text{mg/tablet}} = 4\
\text{tablets}.2 g×1 g1000 mg×500 mg1 tablet
=500 mg/tablet2000 mg=4 tablets. Units cancel (g → mg →
tablet). Whole-number conversions produce 2000 mg ÷ 500 mg
= 4. This dose is appropriate given the order and requires no
rounding.
Rationale — Incorrect:
A. (2 tablets) — Represents halving: 2000 mg ÷ 1000 mg (wrong
tablet strength), incorrect unit cancellation. Unsafe underdose.
B. (3 tablets) — Likely from 2000 ÷ 3 ≈ 667 mg assumption or
decimal truncation; indicates calculation error (non-integer
tablet assumption). Unsafe/incorrect.
D. (5 tablets) — Likely from 250 mg misread or addition error;
would give 2500 mg (overdose).
Teaching point: Convert units to the same base (g → mg) before
dividing by strength.
Citation: Horntvedt, T. (3rd ed.). Dimensional Analysis:
Calculating Dosages Safely. Ch. 1.
,2)
Reference: Ch. 1 — Whole Numbers — Adding Whole Numbers
Stem: A nurse is preparing a once-daily pill tray. Orders:
metformin 500 mg PO BID and simvastatin 20 mg PO qHS. The
pharmacy delivered metformin 500 mg tablets and simvastatin
20 mg tablets. For the 24-hour medication count, how many
total tablets will be placed in the tray? (Use whole-number
addition.)
Options:
A. 3 tablets
B. 4 tablets
C. 5 tablets
D. 6 tablets
Correct answer: B. 4 tablets
Rationale — Correct (B):
Metformin 500 mg BID = 2 tablets/day (500 mg each, two
doses). Simvastatin 20 mg qHS = 1 tablet/day. Total = 2 + 1 = 3
tablets — but check: BID means twice daily, and simvastatin
qHS is once nightly -> total 3. Wait—option mismatch; correct
calculation yields 3 tablets. (Correction: The correct answer is
A. 3 tablets.)
[Adjusted final answer below — correcting to follow
dimensional/addition logic]
Correct answer (revised): A. 3 tablets
, Rationale — Correct (A):
Addition: metformin = 2 tablets/day; simvastatin = 1 tablet/day;
total = 2 + 1 = 3 tablets. Units: tablets are like units — simple
whole-number addition. No conversion or rounding needed.
Rationale — Incorrect:
B. (4 tablets) — Overcounts one extra tablet; common error:
interpreting BID as three times.
C. (5 tablets) — Likely misreading of doses or thinking BID
applies to each med.
D. (6 tablets) — Doubling both meds erroneously; arithmetic
error.
Teaching point: Count like units (tablets) and add totals; clarify
dosing frequency abbreviations.
Citation: Horntvedt, T. (3rd ed.). Dimensional Analysis:
Calculating Dosages Safely. Ch. 1.
3)
Reference: Ch. 1 — Whole Numbers — Subtracting Whole
Numbers
Stem: The med cart contains 30 tablets of oxybutynin 5 mg.
After administering morning doses, 7 tablets remain to be given
throughout the day. A patient receives an additional dose of 1
tablet now. How many tablets remain in stock for the rest of the
day? (Use whole-number subtraction and show dimensional
logic: tablets → tablets.)
