So how are we going to know if the question is a formal or an informal one
I think what you're asking is: how do we know whether the question is addressed (formally) at a single person or at a group. There is no formal/informal distinction when talking to a group, you always use vous.
The distinction between formal 2nd person singular and 2nd person plural is only possible through context.
Sign in to submit your answer
Don't have an account yet? Join today
Test your French to the CEFR standard