These problems are from a very large set of questions about Liars who always lie about everything, and Knights who always tell the truth. Some questions also involve Knaves - people who strictly alternate between lying and telling the truth. (They are of course all indistinguishable from one another by outward appearance, and you must use logic to determine who's who.)
You meet a trio of people, A, B, and C. You know that one of them is a knight, one is a liar, and one is a normal, but you are not sure which is which. Normals tell the truth and lie at random. You are allowed to ask three yes-or-no questions. What three questions can you ask to find out which is which?