Consider whether the questions could form grammatically separate sentences. Do the questions ask about the same thing, different things or different aspects of the same thing? If you split two questions into two sentences, would they still make sense?
Split the questions into separate sentences if they make more sense that way, if they ask about different issues or different aspects or if they form grammatically whole sentences. Place a question mark at the end of each separate sentence that asks a question.
For example, these sentences ask two separate questions: "Did you run away? Where did you hide?" One question asks whether an action occurred, and one asks for more information about the action. The sentence would become clunky and unfocused if you combined the two and asked, "Did you run away and where did you hide?"
Place one single question mark at the end of the sentence, if it makes sense to ask the questions in the same sentence. This method works best when the questions are closely related or when they work together to form one bigger question.
For example, the question "Did you run away and hide?" technically asks about two things -- running and hiding. Both questions, however, focus on essential aspects of one event; they both seek to find out, "What did you do?"
Additionally, phrasing it this way presents a simpler query than, "Did you run away? And then did you hide?"
Place the question mark at the end of one single sentence when you ask a short either-or question.
For example, write, "Did you buy chips or salsa?" Instead of "Did you buy chips? Or salsa?"
If the either-or question is long, then split it into two sentences: "Did you plan to buy chips at the grocery store when you stopped there to buy some milk? Or did you want me to buy them on my way home from work today?"
For an either-or sentence of moderate length, you can use either method. You can write, "Did you buy chips, or did you bake a cake?" Or you can write, "Did you buy chips? Or did you bake a cake?"