This interview question tests how you think, not the final answer.
Ask questions to clarify the scope of the problem in question.
It’s also definitely not an item that can be easily tossed around, so let’s lower bound it by 15lbs.
The average in-between estimate is 30lbs, so we can assume a tire might weigh about 30lbs.
Think about the problem critically and explain to the interviewer beforehand how you’re planning to go about answering the question. You’ve broken down the problem, considered exceptions, and explained your approach.
Now, you actually have to come up with some numbers!
Our approach here will be to estimate the road density for a square mile of the US.
Specifically, given a square mile of the US, how much road is in it?
We can break down this problem into rural and urban square miles, as we’d expect the road density to be substantially different.
Generally, with these estimation questions, there are a variety of great approaches.