Translation:There are about thirty people in this room.
Is it necessary to add "ĉi"?. “en tiu ĉambro" means the same, also works, no? Dankon pro via helpo.
No, it's not necessary, strictly speaking, but within the Duolingo course, it's a good idea to add "ĉi" when translating "here" or "this" because your response is being checked by a machine.