> the ability to come up with a good napkin math estimate for a technical problem doesn't correlate with the ability to actually do the job to solve the problem

> the ability to come up with a good napkin math estimate for a technical problem doesn't correlate with the ability to actually do the job to solve the problem. You realise that that's a very strong (and probably wrong) statement? Those two abilities are obviously distinct, but quite probably positively correlated. So while there are be better interview questions, the answer to this question tells you something about the candidate.