Eight calculations worked end to end, including the dosage forms that actually catch people out. Pick an answer and the working opens.
Every answer links to the guide it comes from, so if one of these catches you out you can read the whole topic rather than memorise a single fact. The full domain is at Order Entry and Processing.
1. Amoxicillin 500 mg PO TID × 7 days. Stock is 250 mg capsules. How many capsules?
Answer: B. Work in doses, not milligrams. Each 500 mg dose is 2 × 250 mg capsules. Three doses a day is 6 capsules a day. Over 7 days that is 42. The commonest error is dividing the total milligrams by the capsule strength and forgetting the frequency. More: Days supply — the method and the forms that catch people
2. Clindamycin 300 mg PO q6h, stock 150 mg capsules. How many capsules in a 24-hour supply?
Answer: C. q6h is four doses in 24 hours. Each 300 mg dose is 2 × 150 mg capsules. 2 × 4 = 8 capsules. Read q6h as 'four times a day' rather than counting hours forward from now — that is what keeps hospital 24-hour supply questions quick. More: Days supply — the method and the forms that catch people
3. Unless told otherwise, how many drops are assumed per millilitre?
Answer: C. The convention is 1 mL = 20 drops, and the exam relies on it for ophthalmic days-supply questions. A 5 mL bottle therefore holds about 100 drops. If a question states a different drop factor, use the stated one — an infusion set's gtt/mL is a separate number entirely. More: Days supply — the method and the forms that catch people
4. Tobramycin ophthalmic, 2 drops in each eye six times daily × 7 days, 5 mL bottles. How many bottles?
Answer: B. 4 drops per dose (both eyes) × 6 doses = 24 drops a day; × 7 days = 168 drops. At 20 drops per mL that is 8.4 mL, which is 1.68 bottles. Round UP to 2. Ophthalmic dispensing always rounds up, because loss during administration is expected — rounding down leaves the patient short mid-course. More: Days supply — the method and the forms that catch people
5. Round 7.84621 to the nearest hundredth.
Answer: B. The hundredths place is the second decimal, 4. Look one place to its right: 6, which is 5 or greater, so round up to 7.85. Tenths would give 7.8 and thousandths 7.846 — the exam offers all three, so read which place is asked for before doing anything. More: Days supply — the method and the forms that catch people
6. A calculation gives 3.847 mL, to be measured in a 5 mL oral syringe marked every 0.5 mL. What should you do?
Answer: B. Practical rounding: the answer has to be measurable with the device in hand. A syringe marked in 0.5 mL increments cannot deliver 3.847 mL, so the arithmetic being right does not make the answer usable. The same rule stops you reporting 7.3 days when the prescription is written in whole days. More: Days supply — the method and the forms that catch people
7. Diphenhydramine is dosed 5 mg/kg/day. A child weighs 35 lb. What is the daily dose?
Answer: A. Convert first: 35 lb ÷ 2.2 = 15.9 kg. Then 5 mg × 15.9 = 79.5 mg/day. Set it up so the units cancel — mg = (5 mg/kg/day) × (1 kg / 2.2 lb) × 35 lb × 1 day — and the pounds disappear, leaving mg. The 175 mg option is what you get by forgetting to convert at all. More: Days supply — the method and the forms that catch people
8. What is the first step of dimensional analysis?
Answer: B. Write the target unit first, then arrange every given value and conversion factor so that all other units cancel, and do the arithmetic last. Setting the target first is what makes the cancellation a check on your setup: if the units do not cancel to what was asked for, the setup is wrong and no amount of correct arithmetic will save it. More: Days supply — the method and the forms that catch people
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