Nous sommes dix-sept dans la salle.

Because French uses être in this kind of sentence to express how many people are in a group.

So Nous sommes dix-sept literally looks like We are seventeen, but the natural meaning is There are seventeen of us or We are seventeen people.

Using avoir here would be wrong. French does not say Nous avons dix-sept to mean There are seventeen of us.

Here, dix-sept means seventeen people.

French often leaves out the noun when it is obvious. So:

• Nous sommes dix-sept = There are seventeen of us
• more explicitly: Nous sommes dix-sept personnes

In this sentence, dix-sept is not just a number floating on its own; it is telling you the size of the group.

Because French does not need it here.

When the subject is already a group of people, personnes is often omitted:

• Nous sommes dix-sept.
• Vous êtes combien ? — Nous sommes dix-sept.

You can say Nous sommes dix-sept personnes, but it is less necessary unless you want to be extra clear or slightly more formal.

Both are possible, but they do slightly different things.

• Nous sommes dix-sept dans la salle. = There are seventeen of us in the room.
• Il y a dix-sept personnes dans la salle. = There are seventeen people in the room.

The first version includes the speaker as part of the group and focuses on us.
The second version is a more neutral statement about how many people are present.

So if you are one of the seventeen, nous sommes dix-sept is very natural.

It means in the room, in the hall, or sometimes in the classroom, depending on context.

The noun salle is broader than English room in some cases. It can refer to:

• a room
• a hall
• a classroom
• a function room
• a larger indoor space

So the exact English translation depends on the situation.

That is a very normal position in French. The basic structure is:

• Nous sommes dix-sept = there are seventeen of us
• dans la salle = in the room

Putting the location at the end sounds natural and straightforward.

You could also move it for emphasis:

• Dans la salle, nous sommes dix-sept.

But Nous sommes dix-sept dans la salle is perfectly normal.

Yes. In everyday spoken French, on is often used instead of nous:

• On est dix-sept dans la salle.

This is very common in speech.

The version with nous sommes is more standard and more common in careful speech or writing, but both are correct.

No. It stays dix-sept.

Most French numbers are invariable, so they do not change form here. You do not add -s in this sentence.

So the correct form is:

• Nous sommes dix-sept dans la salle.

not

• Nous sommes dix-septs dans la salle.

A careful pronunciation would be roughly:

nou som diz-set dan la sal

More precisely:

• Nous → nou
• sommes → som
• dix-sept → dis-set
• dans → nasal vowel, something like dahn
• la salle → la sal

A useful point: in dix-sept, the x is pronounced like an s sound: dis-set.

Usually yes.

Dans la salle normally means the people are present in the room. So the sentence is typically understood as a count of the people currently there.

If the context changed, it could refer to who is in that room as a group at some given moment, but the most natural reading is simply: there are seventeen of us in the room.

Yes.

These are all possible, with slightly different emphasis:

• Nous sommes dix-sept dans la salle. = There are seventeen of us in the room.
• Nous sommes dix-sept dans cette salle. = There are seventeen of us in this room.
• Nous sommes dix-sept ici. = There are seventeen of us here.

They all work; the choice depends on what location you want to highlight.