GP Maths Problems
Real world maths problems are messier than GCSE questions
08 May 2026
I enjoy discovering maths problems that feature in the professional lives of adults, and a GP has helpfully sent me some examples that have cropped up in her surgery recently.
Here's one of them:
A patient in A&E was issued 250mg of phenoxymethylpenicillin (penV) four times a day for 5 days from the hospital pharmacy, and requires another 5 days from the GP. How many mls of penV should I prescribe, at 250mg per 5ml?
The arithmetic is simple*, but like a GCSE word problem it needs a clear head to work out what it means, break the problem down into steps and come up with the right answer. You don't want to prescribe ten times too much by accident.
I mentioned it to another GP last night. He said: "I often have to tackle this sort of prescription problem while a patient is sitting there. I sometimes wish I was able to just pop out to a quiet space, take a deep breath and work on it in silence."
Real-world maths isn’t always neat, it's often surrounded by redundant information, technical language, and has real consequences if you get it wrong.
*I make it 100mL, but I'm glad I'm not the GP putting my name to it.
NUMBERS FOR GPs WORKSHOP
In June, I'm doing a workshop at an NHS conference for GPs. I'm calling my session 'Numbers for GPs'. It's the second time I've done a workshop like this, there's a description of the first one here: https://robeastaway.com/blog/gp-maths
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