Problem posted during our class on April 8:

There are four types of people:
boy knight and girl knave always tell truth;  boy knave and girl knight always lie.

There is one guilty person, which can be A, B, or C.  We want to find out who s/he is.

The judge has the following conversation with these three people:

Judge to A: Who is the guilty person?
A: He is a boy.
Judge to A: Is he a knight or knave?
A: He is a knave.

Judge to B: What do you know about A?
B: She is a girl.
Judge to B: Is she a knight or knave?
B: She is a knave.

Judge to C: Are you the guilty person?
C: (answers Judge privately, so we cannot hear if it is yes or no).
Judge: Now I know who is the guilty person.

Based on the above information we should figure out who is the guilty person.

Hints:

1. Which type of person (knight or knave, boy or girl) can A be?

2. Which type is the guilty person?

3.  If C answers yes, can we narrow down to one possibility regarding who is the guilty person?

4. If C answers no, can we narrow down to one possibility regarding who is the guilty person?