Four friends, Edwin, Fred, Gary and Howard, were playing together  when one of them broke a vase.  The teacher asked: "Who is the culprit?"  Both Edwin and Howard said, "Not me."  Fred said, "Howard broke the vase."  Gary said, "Fred is the culprit."  If only one of four boys was lying,~\uline{~~~~~~~~~~}~broke the vase. 
Overseas Competition->Knowledge Point->Counting Modules->Permutations and Combinations->Combinations
Either Fred or Howard must be lying since what they said did not tally.  Since only one person was lying, Gary was telling the truth i.e, Fred broke the vase. 