On an island there are two types of inhabitants: Heroes who always tell the truth and Villains who always lie. Four inhabitants are seated around a table. When each is asked "Are you a Hero or a Villain?", all four reply "Hero". When asked "Is the person on your right a Hero or a Villain?", all four reply "Villain". How many Heroes are present?
(A) 0
(B) 1
(C) 2
(D) 3
(E) 4
First, we note that no matter how many Heroes are present, all four would always reply "Hero" when asked "Are you a Hero or a Villain?". (This is because Heroes will tell the truth and answer "Hero" and Villains will lie and answer "Hero".)

When each is asked "Is the person on your right a Hero or a Villain?", all four reply "Villain", so any Hero that is at the table must have a Villain on his right (or he would have answered "Hero") and any Villain at the table must have a Hero on his right (or he would have had a Villain on his right and answered "Hero").

In other words, Heroes and Villains must alternate around the table, so there are 2 Heroes and 2 Villains.

(It is worth checking that when 2 Heroes and 2 Villains sit in alternate seats, the answers are indeed as claimed.)

ANSWER: (C)