Dimensional Analysis
Calculating Dosages Safely
3rd Edition
• Author(s)Tracy Horntvedt
TEST BANK
1
Reference
Ch. 1 — Types of Numbers / Whole Numbers
Stem
The provider orders acetaminophen 1000 mg PO q6h PRN for
fever. The unit stock has 500 mg tablets. How many tablets
should the nurse give for one dose? (Use dimensional analysis.)
A. 1 tablet
B. 2 tablets
,C. 3 tablets
D. 4 tablets
Correct answer: B. 2 tablets
Rationale — Correct (B)
Dimensional analysis: 1000 mg×1 tablet500 mg=2 tablets1000\
\text{mg} \times \dfrac{1\ \text{tablet}}{500\ \text{mg}} = 2\
\text{tablets}1000 mg×500 mg1 tablet=2 tablets. Unit mg
cancels, leaving tablets. Whole-number result; no rounding
needed. Two tablets delivers the ordered 1000 mg and is safe
per the order.
Rationale — Incorrect
A. (1 tablet) = 500 mg — underdose; error: failed to convert to
correct tablet strength.
C. (3 tablets) = 1500 mg — overadministers by 500 mg; error:
multiplying instead of dividing by tablet strength.
D. (4 tablets) = 2000 mg — double the ordered dose; error:
incorrect multiplication or mixing mg and tablet units.
Teaching point: Always convert ordered dose to supply units
and cancel matching units first.
Citation: Horntvedt, T. (3rd ed.). Dimensional Analysis:
Calculating Dosages Safely. Ch. 1.
2
,Reference
Ch. 1 — Adding Whole Numbers
Stem
A patient receives amoxicillin 250 mg PO every 8 hours for 5
days. How many milligrams total will the patient receive over
the full 5-day course? (Use dimensional analysis; whole-number
arithmetic.)
A. 3,000 mg
B. 3,750 mg
C. 4,500 mg
D. 5,000 mg
Correct answer: C. 4,500 mg
Rationale — Correct (C)
Per day: every 8 hours = 3 doses/day. Total doses = 3×5=153
\times 5 = 153×5=15 doses. Total mg = 250 mg×15=3,750250\
\text{mg} \times 15 = 3,750250 mg×15=3,750 → Wait check: we
must recalc carefully. Important: do digit-by-digit arithmetic.
250 × 15 = 3,750 mg. Oops — correct math yields 3,750 mg.
Therefore the correct answer is B. (See corrected below.)
[Correction applied — final correct answer and rationale
below]
Correct answer (final): B. 3,750 mg
Rationale — Correct (B)
Doses per day = 24 hr ÷ 8 hr = 3 doses/day. Total doses over 5
days = 3×5=153 \times 5 = 153×5=15. Total mg =
, 250 mg/dose×15 doses=3,750 mg250\ \text{mg/dose} \times
15\ \text{doses} = 3,750\
\text{mg}250 mg/dose×15 doses=3,750 mg. All operations use
whole numbers; no rounding required.
Rationale — Incorrect
A. (3,000 mg) = 12 doses assumed (error: 3 doses/day × 4 days).
C. (4,500 mg) = 18 doses assumed (error: 3 doses/day × 6 days).
D. (5,000 mg) = arithmetic error or incorrect dose/day
calculation.
Teaching point: Convert dosing frequency to total doses
(doses/day × days) before multiplying by per-dose amount.
Citation: Horntvedt, T. (3rd ed.). Dimensional Analysis:
Calculating Dosages Safely. Ch. 1.
3
Reference
Ch. 1 — Subtracting Whole Numbers
Stem
A med cart contained 200 tablets of drug X at shift start. During
the shift a nurse administered five 2-tablet doses and one
single-tablet dose. How many tablets remain in the cart? (Use
dimensional analysis and whole-number subtraction.)
A. 188 tablets
B. 187 tablets
Calculating Dosages Safely
3rd Edition
• Author(s)Tracy Horntvedt
TEST BANK
1
Reference
Ch. 1 — Types of Numbers / Whole Numbers
Stem
The provider orders acetaminophen 1000 mg PO q6h PRN for
fever. The unit stock has 500 mg tablets. How many tablets
should the nurse give for one dose? (Use dimensional analysis.)
A. 1 tablet
B. 2 tablets
,C. 3 tablets
D. 4 tablets
Correct answer: B. 2 tablets
Rationale — Correct (B)
Dimensional analysis: 1000 mg×1 tablet500 mg=2 tablets1000\
\text{mg} \times \dfrac{1\ \text{tablet}}{500\ \text{mg}} = 2\
\text{tablets}1000 mg×500 mg1 tablet=2 tablets. Unit mg
cancels, leaving tablets. Whole-number result; no rounding
needed. Two tablets delivers the ordered 1000 mg and is safe
per the order.
Rationale — Incorrect
A. (1 tablet) = 500 mg — underdose; error: failed to convert to
correct tablet strength.
C. (3 tablets) = 1500 mg — overadministers by 500 mg; error:
multiplying instead of dividing by tablet strength.
D. (4 tablets) = 2000 mg — double the ordered dose; error:
incorrect multiplication or mixing mg and tablet units.
Teaching point: Always convert ordered dose to supply units
and cancel matching units first.
Citation: Horntvedt, T. (3rd ed.). Dimensional Analysis:
Calculating Dosages Safely. Ch. 1.
2
,Reference
Ch. 1 — Adding Whole Numbers
Stem
A patient receives amoxicillin 250 mg PO every 8 hours for 5
days. How many milligrams total will the patient receive over
the full 5-day course? (Use dimensional analysis; whole-number
arithmetic.)
A. 3,000 mg
B. 3,750 mg
C. 4,500 mg
D. 5,000 mg
Correct answer: C. 4,500 mg
Rationale — Correct (C)
Per day: every 8 hours = 3 doses/day. Total doses = 3×5=153
\times 5 = 153×5=15 doses. Total mg = 250 mg×15=3,750250\
\text{mg} \times 15 = 3,750250 mg×15=3,750 → Wait check: we
must recalc carefully. Important: do digit-by-digit arithmetic.
250 × 15 = 3,750 mg. Oops — correct math yields 3,750 mg.
Therefore the correct answer is B. (See corrected below.)
[Correction applied — final correct answer and rationale
below]
Correct answer (final): B. 3,750 mg
Rationale — Correct (B)
Doses per day = 24 hr ÷ 8 hr = 3 doses/day. Total doses over 5
days = 3×5=153 \times 5 = 153×5=15. Total mg =
, 250 mg/dose×15 doses=3,750 mg250\ \text{mg/dose} \times
15\ \text{doses} = 3,750\
\text{mg}250 mg/dose×15 doses=3,750 mg. All operations use
whole numbers; no rounding required.
Rationale — Incorrect
A. (3,000 mg) = 12 doses assumed (error: 3 doses/day × 4 days).
C. (4,500 mg) = 18 doses assumed (error: 3 doses/day × 6 days).
D. (5,000 mg) = arithmetic error or incorrect dose/day
calculation.
Teaching point: Convert dosing frequency to total doses
(doses/day × days) before multiplying by per-dose amount.
Citation: Horntvedt, T. (3rd ed.). Dimensional Analysis:
Calculating Dosages Safely. Ch. 1.
3
Reference
Ch. 1 — Subtracting Whole Numbers
Stem
A med cart contained 200 tablets of drug X at shift start. During
the shift a nurse administered five 2-tablet doses and one
single-tablet dose. How many tablets remain in the cart? (Use
dimensional analysis and whole-number subtraction.)
A. 188 tablets
B. 187 tablets
