It's not about getting the "right" answer, it's about how you approach tackling the problem. If you talk through your solution as you do it, no one is going to

It's not about getting the "right" answer, it's about how you approach tackling the problem. If you talk through your solution as you do it, no one is going to question which assumption you make. The assumptions are baked into the answer, but part of the point of these kinds of questions is that they don't matter that much. Or more to the point, the uncertainty in your answer is on the order of the uncertainty of your assumptions, which hardly matter whether you assume a 25 ft bus or a 50 ft bus, if you think the precision of you answer justifies confidence better than a factor of 2, you don't understand the problem as well as you think you do. And the seats really don't matter, volume-wise. Unless you're actually counting the golf balls, which, I agree, would be silly.