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Whose Footprints?
 
Q One of the triplets left muddy footprints all over the kitchen floor. Since all three wear the same size shoes, their mom and dad can't tell which triplet should clean up the floor. "I didn't do it," said Annie. "Danny did it," said Fanny. "Fanny is lying," said Danny. Only one of the triplets is telling the truth ? the other two are lying.

Whose footprints are on the kitchen floor?


 
A Annie left the footprints. Remember, only one triplet can be telling the truth. If Danny did it, then both Fanny and Annie are telling the truth. If Fanny did it, then Danny is telling the truth when he says that Fanny is lying. With Annie as the culprit, Annie is lying by claiming she is innocent, Fanny is lying by accusing Danny, and Danny is the one who is telling the truth.

Source: Usborne Brain Puzzles, p. 10