In a small village there are two kinds of people: liars and truthtellers.
Everybody knows everybody and everybody knows as well who is a liar and who’s a truth-teller.
I approach six villagers and pose the same question to each of them:
"How many liars are among you?"
I get six distinct answers (integers, of course) and deduce the true one.
How many liars are in that group?
Liars always lie and truthtellers never do.
(In reply to re: Summing up - spoiler
by Dej Mar)
You are absolutely right.
I knew that one can say 6 only if there is a truth teller in the group so
the option "no 5 but with 6 " (your d.) does not exist.
Somehow when I wrote my "sum up" - forgo to mention it.
Since there is no way to correct the "official" version I am going to edit my comment and post a disclaimer re : "official answer".
Tnx for your comment.