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A merchant bought 4 watches from a craftsman . On his way home he opened the box containing his purchase. He realized that one is telling a wrong time then notice one of them is not running while one of them is running at different speed..only one always tell the right time. He returned all the watches inside the box and brought it back to the craftsman. When the box was opened for complaint the craftsman told the merchant that none of the watches in that box tells the wrong time. The merchant believed him and went back home without replacement or fixing of his purchase. Wearing the watch that always tell the right time ,when he got home the other watches in the box tells the right time. Is there some explanation for this?