When a hotel gives a description of the rooms in the facility, which sentence is correct and why?
All the rooms are equipped with a free internet connection.
All rooms are equipped with a free internet connection.
When a hotel gives a description of the rooms in the facility, which sentence is correct and why?
All the rooms are equipped with a free internet connection.
All rooms are equipped with a free internet connection.
In ordinary speech and writing, I would say "all the rooms".
In a promotional context "all rooms" is common.
Both are correct, because both are idiomatic shortenings of grammatically correct sentences. The elided words are clear from the context. The sentence
All the rooms are equipped with a free internet connection.
is a concise expression of the more verbose sentence
All [of] the rooms [in this hotel] are equipped with a free internet connection.
Likewise, the sentence
All rooms are equipped with a free internet connection.
is a shortened version of the sentence
[In this hotel,] all rooms are equipped with a free internet connection.
There are other possible "source" sentences, but to me, these seem to be the most likely candidates.