Dimensional Analysis
Calculating Dosages Safely
3rd Edition
• Author(s)Tracy Horntvedt
TEST BANK
1)
Reference
Ch. 1 — Whole Numbers: Multiplying & Dividing Whole
Numbers
Stem
A provider orders amoxicillin 500 mg PO every 8 hours for 5
days. The pharmacy supplies 250 mg scored tablets. Using
dimensional analysis, how many whole tablets should the nurse
give per single dose at the bedside?
Options
A. 1 tablet
,B. 2 tablets
C. 3 tablets
D. 4 tablets
Correct answer: B. 2 tablets
Rationale — Correct (B)
Setup: 500 mg × (1 tablet / 250 mg) = 500/250 = 2 tablets. Unit
cancellation: mg cancels, leaving tablets. This is a simple
division resulting in a whole number — no rounding required.
Two tablets per dose is safe and matches the ordered 500 mg.
Rationale — Incorrect
A (1 tablet): Mistakenly halved the dose (500 mg ÷ 2 = 250 mg);
inversion error. Unsafe underdose.
C (3 tablets): Likely calculation error (3 × 250 = 750 mg), would
overdose by 250 mg.
D (4 tablets): Overestimation (4 × 250 = 1000 mg), unsafe
overdose.
Teaching point: Always set up mg → tablets (one tablet = X mg)
and cancel units before computing.
Citation: Horntvedt, T. (3rd ed.). Dimensional Analysis:
Calculating Dosages Safely. Ch. 1.
2)
Reference
Ch. 1 — Whole Numbers: Adding Whole Numbers
,Stem
Patient will receive metformin 500 mg PO twice daily for 7
days. Supply: 500 mg tablets. How many tablets total will the
patient take over the 7-day course?
Options
A. 7 tablets
B. 10 tablets
C. 14 tablets
D. 28 tablets
Correct answer: C. 14 tablets
Rationale — Correct (C)
Twice daily = 2 tablets/day. Total = 2 tablets/day × 7 days = 14
tablets. Dimensional analysis: (tablets/day) × (days) → tablets;
whole-number multiplication.
Rationale — Incorrect
A (7): Missed second daily dose (1 × 7).
B (10): Possibly used 5 days instead of 7 (2 × 5 = 10).
D (28): Doubled twice daily again (4 × 7) — common
multiplication error.
Teaching point: Multiply frequency by duration; keep units
(tablets/day × days → tablets).
Citation: Horntvedt, T. (3rd ed.). Dimensional Analysis:
Calculating Dosages Safely. Ch. 1.
, 3)
Reference
Ch. 1 — Whole Numbers: Subtracting Whole Numbers
Stem
A nurse has an inventory of 120 insulin pens. During a clinic
day, 37 pens are dispensed. How many pens remain in stock at
day’s end?
Options
A. 83 pens
B. 87 pens
C. 93 pens
D. 103 pens
Correct answer: B. 83 pens
Rationale — Correct (A)
120 − 37 = 83 pens remaining. (Note: correct answer is A — 83
pens.) Dimensional setup: pens_total − pens_dispensed =
pens_remaining.
Rationale — Incorrect
B (87): Likely subtracted incorrectly (120 − 33 = 87) — digit
error.
C (93): Possibly subtracted 27 instead of 37 (120 − 27).
D (103): Possibly subtracted 17 (120 − 17).
Teaching point: Perform integer subtraction carefully; line up
digits to avoid place-value mistakes.
Calculating Dosages Safely
3rd Edition
• Author(s)Tracy Horntvedt
TEST BANK
1)
Reference
Ch. 1 — Whole Numbers: Multiplying & Dividing Whole
Numbers
Stem
A provider orders amoxicillin 500 mg PO every 8 hours for 5
days. The pharmacy supplies 250 mg scored tablets. Using
dimensional analysis, how many whole tablets should the nurse
give per single dose at the bedside?
Options
A. 1 tablet
,B. 2 tablets
C. 3 tablets
D. 4 tablets
Correct answer: B. 2 tablets
Rationale — Correct (B)
Setup: 500 mg × (1 tablet / 250 mg) = 500/250 = 2 tablets. Unit
cancellation: mg cancels, leaving tablets. This is a simple
division resulting in a whole number — no rounding required.
Two tablets per dose is safe and matches the ordered 500 mg.
Rationale — Incorrect
A (1 tablet): Mistakenly halved the dose (500 mg ÷ 2 = 250 mg);
inversion error. Unsafe underdose.
C (3 tablets): Likely calculation error (3 × 250 = 750 mg), would
overdose by 250 mg.
D (4 tablets): Overestimation (4 × 250 = 1000 mg), unsafe
overdose.
Teaching point: Always set up mg → tablets (one tablet = X mg)
and cancel units before computing.
Citation: Horntvedt, T. (3rd ed.). Dimensional Analysis:
Calculating Dosages Safely. Ch. 1.
2)
Reference
Ch. 1 — Whole Numbers: Adding Whole Numbers
,Stem
Patient will receive metformin 500 mg PO twice daily for 7
days. Supply: 500 mg tablets. How many tablets total will the
patient take over the 7-day course?
Options
A. 7 tablets
B. 10 tablets
C. 14 tablets
D. 28 tablets
Correct answer: C. 14 tablets
Rationale — Correct (C)
Twice daily = 2 tablets/day. Total = 2 tablets/day × 7 days = 14
tablets. Dimensional analysis: (tablets/day) × (days) → tablets;
whole-number multiplication.
Rationale — Incorrect
A (7): Missed second daily dose (1 × 7).
B (10): Possibly used 5 days instead of 7 (2 × 5 = 10).
D (28): Doubled twice daily again (4 × 7) — common
multiplication error.
Teaching point: Multiply frequency by duration; keep units
(tablets/day × days → tablets).
Citation: Horntvedt, T. (3rd ed.). Dimensional Analysis:
Calculating Dosages Safely. Ch. 1.
, 3)
Reference
Ch. 1 — Whole Numbers: Subtracting Whole Numbers
Stem
A nurse has an inventory of 120 insulin pens. During a clinic
day, 37 pens are dispensed. How many pens remain in stock at
day’s end?
Options
A. 83 pens
B. 87 pens
C. 93 pens
D. 103 pens
Correct answer: B. 83 pens
Rationale — Correct (A)
120 − 37 = 83 pens remaining. (Note: correct answer is A — 83
pens.) Dimensional setup: pens_total − pens_dispensed =
pens_remaining.
Rationale — Incorrect
B (87): Likely subtracted incorrectly (120 − 33 = 87) — digit
error.
C (93): Possibly subtracted 27 instead of 37 (120 − 27).
D (103): Possibly subtracted 17 (120 − 17).
Teaching point: Perform integer subtraction carefully; line up
digits to avoid place-value mistakes.
