There are an infinite number of variations on the problem; you could also ask about a reservoir with inflows and outflows, or a water tower, or a continuous distillation process. I think the money variant is actually one of the worst, as it evokes no imagery (in an era of largely digital transactions), but I'm not sure the exact question asked really matters.

If someone fights a hypothetical, they're usually being adversarial, confrontational, or just avoiding answering the question, which is useful information in an interview.