You are at one end of a hall blindfolded. At the other end are Alex and Bert. You are allowed to ask any yes or no questions you want, but only one of them will respond. They are standing next to each other and their voices are identical, so you have no way of telling which one responded by sound alone.
Using as few questions as possible, find out the type of each Alex and Bert and who answered your last question.
Q1. Am I blindfolded? (If Yes, at least 1 knight, if No at least 1 liar)
Q2. Is the person next to you a liar? (If Q1=Yes & Q2= No then there are 2 knights; if Q1=No & Q2 = No then 2 liars; else 1 of each)
Q3 A. Are you Bert? (Ask this if both are liars or knights - then its solved.)
Q3 B. Is Bert a liar? (If Q3=Yes, then Bert is speaking. If No, Alex is speaking.)
Q4. Did you answer the previous question? (now we have a table with Q3 & Q4 answers. If both Q3 & Q4 are No or if both are Yes, then Bert is a liar. Otherwise Bert is a knight.)
Q5. Is Bert a liar? (this repeats a question, but it also lets you know who is talking. And so its solved.)
5 questions or less
