Dimensional Analysis
Calculating Dosages Safely
3rd Edition
• Author(s)Tracy Horntvedt
TEST BANK
1
Reference
Ch. 1 — Whole Numbers: Adding Whole Numbers
Stem
A provider orders ondansetron 8 mg PO now. The unit stock
contains 4 mg tablets. Using dimensional analysis, how many
tablets should the nurse give? (Tablets are whole and may be
given as whole tablets only.)
A. 1 tablet
B. 2 tablets
,C. 4 tablets
D. 8 tablets
Correct Answer: B
Rationale — Correct (B)
Set up: 8 mg×1 tablet4 mg=2 tablets8\text{ mg} \times
\frac{1\text{ tablet}}{4\text{ mg}} = 2\text{
tablets}8 mg×4 mg1 tablet=2 tablets. Units cancel mg → tablets.
With whole-tablet requirement, 2 whole tablets is exact and
safe. No rounding required.
Rationale — Incorrect
A (1 tablet): Uses 1 tablet (4 mg) — underdose by 4 mg (simple
subtraction error).
C (4 tablets): Multiplies instead of dividing → 16 mg (inversion
error).
D (8 tablets): Confuses mg and tablet count (placing order
number as tablet count).
Teaching Point:
Set unit fraction so mg cancels; check whole-tablet rules before
rounding.
Citation:
Horntvedt, T. (3rd ed.). Dimensional Analysis: Calculating
Dosages Safely. Ch. 1.
2
,Reference
Ch. 1 — Whole Numbers: Subtracting Whole Numbers
Stem
A nurse prepares a 24-hour oral medication schedule. A patient
receives 6 tablets daily; at 0600 the patient already took 2
tablets. How many whole tablets remain to be given for the rest
of the day?
A. 2 tablets
B. 4 tablets
C. 6 tablets
D. 8 tablets
Correct Answer: B
Rationale — Correct (B)
Total daily = 6 tablets. Remaining = 6−2=46 - 2 = 46−2=4 tablets.
Dimensional reasoning: tablets are the unit throughout;
subtraction of whole numbers provides remainder to schedule.
Rationale — Incorrect
A (2): Mistakes taken as remaining (misreads order).
C (6): Ignores the two already given.
D (8): Adds rather than subtracts — an arithmetic inversion
error.
Teaching Point:
Keep units constant; subtract only after confirming total
ordered and dose already given.
, Citation:
Horntvedt, T. (3rd ed.). Dimensional Analysis: Calculating
Dosages Safely. Ch. 1.
3
Reference
Ch. 1 — Whole Numbers: Multiplying Whole Numbers
Stem
Provider orders prednisone 20 mg PO daily. Supply: 5 mg
tablets. How many tablets per day must the nurse administer
using dimensional analysis?
A. 2 tablets
B. 3 tablets
C. 4 tablets
D. 5 tablets
Correct Answer: C
Rationale — Correct (C)
Set up: 20 mg×1 tablet5 mg=4 tablets20\text{ mg} \times
\frac{1\text{ tablet}}{5\text{ mg}} = 4\text{
tablets}20 mg×5 mg1 tablet=4 tablets. mg cancels leaving
tablets. Exact whole number; no rounding.
Rationale — Incorrect
A (2): Under-calculation by factor of 2 (divided by 10 instead of
5).
Calculating Dosages Safely
3rd Edition
• Author(s)Tracy Horntvedt
TEST BANK
1
Reference
Ch. 1 — Whole Numbers: Adding Whole Numbers
Stem
A provider orders ondansetron 8 mg PO now. The unit stock
contains 4 mg tablets. Using dimensional analysis, how many
tablets should the nurse give? (Tablets are whole and may be
given as whole tablets only.)
A. 1 tablet
B. 2 tablets
,C. 4 tablets
D. 8 tablets
Correct Answer: B
Rationale — Correct (B)
Set up: 8 mg×1 tablet4 mg=2 tablets8\text{ mg} \times
\frac{1\text{ tablet}}{4\text{ mg}} = 2\text{
tablets}8 mg×4 mg1 tablet=2 tablets. Units cancel mg → tablets.
With whole-tablet requirement, 2 whole tablets is exact and
safe. No rounding required.
Rationale — Incorrect
A (1 tablet): Uses 1 tablet (4 mg) — underdose by 4 mg (simple
subtraction error).
C (4 tablets): Multiplies instead of dividing → 16 mg (inversion
error).
D (8 tablets): Confuses mg and tablet count (placing order
number as tablet count).
Teaching Point:
Set unit fraction so mg cancels; check whole-tablet rules before
rounding.
Citation:
Horntvedt, T. (3rd ed.). Dimensional Analysis: Calculating
Dosages Safely. Ch. 1.
2
,Reference
Ch. 1 — Whole Numbers: Subtracting Whole Numbers
Stem
A nurse prepares a 24-hour oral medication schedule. A patient
receives 6 tablets daily; at 0600 the patient already took 2
tablets. How many whole tablets remain to be given for the rest
of the day?
A. 2 tablets
B. 4 tablets
C. 6 tablets
D. 8 tablets
Correct Answer: B
Rationale — Correct (B)
Total daily = 6 tablets. Remaining = 6−2=46 - 2 = 46−2=4 tablets.
Dimensional reasoning: tablets are the unit throughout;
subtraction of whole numbers provides remainder to schedule.
Rationale — Incorrect
A (2): Mistakes taken as remaining (misreads order).
C (6): Ignores the two already given.
D (8): Adds rather than subtracts — an arithmetic inversion
error.
Teaching Point:
Keep units constant; subtract only after confirming total
ordered and dose already given.
, Citation:
Horntvedt, T. (3rd ed.). Dimensional Analysis: Calculating
Dosages Safely. Ch. 1.
3
Reference
Ch. 1 — Whole Numbers: Multiplying Whole Numbers
Stem
Provider orders prednisone 20 mg PO daily. Supply: 5 mg
tablets. How many tablets per day must the nurse administer
using dimensional analysis?
A. 2 tablets
B. 3 tablets
C. 4 tablets
D. 5 tablets
Correct Answer: C
Rationale — Correct (C)
Set up: 20 mg×1 tablet5 mg=4 tablets20\text{ mg} \times
\frac{1\text{ tablet}}{5\text{ mg}} = 4\text{
tablets}20 mg×5 mg1 tablet=4 tablets. mg cancels leaving
tablets. Exact whole number; no rounding.
Rationale — Incorrect
A (2): Under-calculation by factor of 2 (divided by 10 instead of
5).
