If you're a poor kid who's never been skiing, you'll have a harder time conceptualizing the answer.
The question reminds me of "how many groves are there on a vinyl record?"
If I ask you how many sugars you want in your coffee and you answer with an equation I will assume you're joking or an idiot :)
Clearly, it's a trick question (with unnecessary details to distract you from a possible solution) and the one asking probably thinks they are very clever. So now, whether you accept an equation or insist that it's impossible to solve when it's not really comes down to how you want to play that game.
The "twist" on the answer is that you start below all the other chairs and finish above all the other chairs, so you must have passed them all along the way. I saw this immediately and answered "99" or whatever it was. In retrospect, I think they couldn't conceive of anyone figuring it out on the fly.
Imagine there's a circle with marks evenly spaced, eg roots of unity. When you rotate it halfway, the point that started at the bottom has passed (vertically) all the other points ahead of it, because at some stage each point has reached the top and started going down.
I suspect the answer to this is "not enough information", which, I suppose, hints at an applicants requirements gathering thought process?
The question: You get on a ski lift going up. It's 1000m long and you move at 20m/s. Between when you get on at the bottom and you get off at the top, how many of the chairs going down do you pass?