How should I phrase a question that must be answered with an ordinal number (e.g., the third prime)?
Framing a question to which the answer is an ordinal number
How to ask a question to get a cardinal number answer
Assume that there are 5 apples must be eaten by Jack. When you want to know about how many of the apples are eaten, you may ask Jack, 'how many apples have you eaten?'; But how can I ask the question to make Jack answers, 'I'm eating the fourth apple'?