One thing to remember with those analytical questions is that, more often than not, it’s not the final answer that matters but the thought process. I’m sure you’ve been told that before countless number of times, but it IS true.
So I would have gone for somthing like this:
- Estimate number of pubs in Oxford - use and educated guess (pubs/mile -> area of Oxford) or prior knowledge
- Estimate pub turnover (or if figures are not required, say something along the lines of "call a pub, ask how much they make each night, roughly)
- Get a rough average per night -> per hour
Like I say, the interviewers are looking for a person with an ability to take clear, systematic approach and an analytical mind, so even if the final answer is inaccurate (with in reason), but the approach was good, you’re likely to have done well.
Think of it as “method marks” in exam papers.