What is the difference between fragen and nachfragen? The question was to translate:
I would ask.
I translated that as: Ich würde fragen, but it was marked wrong. The correct answer was: Ich würde nachfragen.
What is the difference between fragen and nachfragen? The question was to translate:
I would ask.
I translated that as: Ich würde fragen, but it was marked wrong. The correct answer was: Ich würde nachfragen.
Fragen is a very open act and would be the closest translation to the word "to ask". It can be used almost always as the translation, but sometimes it wouldn't be a good form.
Nachfragen on the other hand is more specific than fragen: it often means that you're asking for confirmation like "Is this true?" or "Did you say that" or "what's my job here?" like Janka stated in his/her comment. Another thing about nachfragen is that it implies interaction in terms of getting an answer: "to ask yourself" would only translate to "sich etwas fragen" (nachfragen would be wrong here). When you use nachfragen you want confirmation/information from another person/group/office/etc.
The simplest separation of those word however is to what/who the asking refers: "Asking someone" is always "fragen". "Asking about a state of something" almost always translates to "nachfragen"
Examples:
Now more generalized:
Italic words are the indicator whether fragen or nachfragen should be used.
As in most things in the German language, there are always some exceptions to this. But it's a good orientation.
To your example: I assume the "I would ask" refers to something said before, and if it's a sentence like "how does this work?" or "when will they come?", which are both asking about a state (functionality/time of the arrival). In that case, it would apply to the former sentences' kind of question and therefore be translated to "ich würde nachfragen".
Depending on the context, nachfragen could be more appropriately translated with to inquire, while fragen to me is more of a direct translation of to ask.
Ich werde mal auf dem Amt nachfragen, wie es mit meinem Antrag steht.
I'll inquire about the status of my application from the bureau.