Hello!

I've bought a penguin active reading book(level 2). No sooner had I started reading than I realized a strange thing. It is the article 'a'. Why is it there? I thought the subject is plural so why 'a'?. The sentence goes like that: A hundred scholars are sitting on the floor in the palace at Xianyang. I am asking because it is not the first time when I see a sentence like that and I do not know the answer.

Sądzę, że tłumaczyć należy:
a hundred = około stu ..., ew. - jakieś sto ..., lub - jakaś setka uczniów ...