20CS110001  Introduction to Computer Science  Fall 2010 

Solution to Double Doors Puzzle
"If I asked the other person, 'Does the left door lead to the
riches?' what would the response be?"
To guarantee a lying response, bring both people into the question's response. This ensures that with one person always telling the truth and one always lying, the answer has to be a lie. Ask either person "If I asked the other person, 'Does the left door lead to the riches?', what would the response be?" To guarantee a truthful response, ask "If I asked the other person, 'Does the left door lead to the riches?' would they say 'no?'"
Suppose it's the left door
Suppose it's the right door
