Sample 1 of 2
Child 22 kg prescribed 5 mg/kg. Available: 250 mg/5 mL. What volume?
Give your answer in mL.
Answer:2.2
Why
Dose = 5 x 22 = 110 mg. Volume = (110/250) x 5 = 550/250 = 2.2 mL.
BNF
Measuring the correct dose
Written and checked against the NMC’s published sources by The NMCMATE editorial team.Last checked .
2 marks of the 15 in Part A, which runs for 30 minutes.
These questions give you a prescription and a stock strength and ask what the patient should actually receive. The arithmetic is not hard on its own. What makes it hard is that the numbers arrive in different units, the calculator is on screen rather than in your hand, and you have around two minutes a question.
What this section asks about
- Dose per kilogram of body weight, then the volume that dose comes to
- Concentrations written as mg/mL, mg in a given volume, or a percentage
- Body mass index from a weight in kilograms and a height in metres
- Rounding to a volume a syringe can actually measure
Where the marks go
2 marks of the 15 in Part A, which runs for 30 minutes.
Every numeracy question sits at the apply and analyse level: you are given a situation and asked to work something out, rather than to recall a fact.
Worked examples
The method, with the answer shown. Practise below once you have the shape of it.
Gentamicin 5 mg/kg is prescribed for a patient weighing 68 kg. The stock is 40 mg in 1 mL. What volume?
- Find the dose first, then turn it into a volume.
- 5 x 68 = 340 mg
- 340 / 40 x 1
Answer: 8.5 mL
Two calculations, not one. Going straight from 5 mg/kg to a volume skips the step where the dose is worked out.
A patient weighs 78 kg and is 1.68 m tall. What is the body mass index, to one decimal place?
- Weight in kilograms, divided by height in metres squared.
- 1.68 x 1.68 = 2.8224
- 78 / 2.8224 = 27.63
Answer: 27.6
Square the height, do not double it. Dividing by 3.36 gives 23.2, which reads like a plausible answer and is not one.
A child weighing 62 kg is prescribed 7.5 mg/kg. The stock is 100 mg in 4 mL. What volume?
- 7.5 x 62 = 465 mg
- 465 / 100 x 4
Answer: 18.6 mL
Carry the full figure through. Rounding 465 to 470 partway gives 18.8 mL, and the error came from the rounding rather than the method.
Where candidates lose marks
- Rounding partway through. Carry the full figure and round once, at the end.
- Dividing the wrong way round. Write the sum as dose required over dose per unit before you touch the calculator.
- Giving an answer no device can measure. If a calculation returns 0.37 mL, check the strength you used.
Sample questions
From our bank, with the explanation as a student sees it. These particular questions are kept out of the mock papers, so reading them here does not use anything up.
Sample 2 of 2
Patient weighs 82 kg and is 1.68 m tall. BMI to 1 decimal place?
Give your answer in kg/m².
Answer:29.1
Why
BMI = 82 / (1.68 x 1.68) = 82 / 2.8224 = 29.1.
NICE CKS
Questions people ask
- Do I get a calculator for the numeracy questions?
- Yes, an on-screen one, along with an erasable note board and a marker. You must not write on the board until the tutorial has finished.
- How precise does the answer have to be?
- You type a number, so give it in the unit the question asks for and to the number of decimal places it asks for. If the question says one decimal place, 26 and 26.04 are both the wrong shape of answer.
Practise this section
Practice is filtered by section, so you can work on this one on its own. Every account gets 10 new questions a day without a card.
This is one of the fifteen sections the paper is built from. Work through the whole thing with the NMC CBT study guide.