in my experience, its sometimes 100% of the time, even after repeated attempts to correct it with more specific prompts. Even on simple problems involving divisions or multiples of numbers from 1 to 10 with one additional operation.
The parent post probably means that it's not a random chance independent of the question, that while for some (many!) types of questions the hallucination rate is low, there exist some questions or groups of questions for which it will systematically provide misleading information.
