PMs on grapevine: what is your favourite question that you usually ask in the interview?

This question is more for senior PMs and above who end up taking lot of interviews.

Why do you ask this question?

My question is around guesstimate, since the product we're building requires lots of data analysis. And I would prefer a PM from a STEM background.

Mostly TAM related: example: Estimate the TAM of an in-car entertainment system for the next generation of internet users