Math Plus Warm Up: Who Is Lying?

Give one or two warm up problems at beginning of every math class. Encourage students' discussions and be open minded to different possible answers.



















Answer:
Ann and Cindy are lying. If Cindy is telling the truth, then Ann and Betty are lying, so Ann's statement is false and Betty should tells the truth, which can not happen, since Betty is a liar. So, Cindy is lying, which means that Ann or Betty are telling the truth, and after reconsideration of their sentences, we conclude that Betty is telling the truth and Ann is lying.