[bayes]

I think "how many golf balls can you get in a double decker bus" is a fair question for assessing whether someone can apply basic maths to a to a real life (i.e. not perfectly defined) problem. If that's a skill the job needs it's a perfectly reasonable question.

[adnam]

I also think it's a fair question, but more about logical reasoning and estimating than basic maths. As an engineer, you could be asked to estimate the number of load balancers needed for X traffic with Y latency - similar problem.

[arethuza]

In my experience of those kinds of problems the catch is finding realistic values for X and Y - often nobody is going to hand them to you on a plate and you must work out a way of estimating them - that is the real skill.