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A rich man named Stuart Laidlaw had been counting his money. When he finished, he accidentally left a $1000.00 bill on his desk but when he returned for it a short while later, it was gone. Only two other persons could have seen the bill. One was the cook; the other was the gardener. The cook told him that she had hidden it for safekeeping under a green book that was on the desk. But when they looked the bill was not there. The gardener said he had found the bill where the cook had left it. He had placed it inside the book, where he thought there was less chance that somebody would find it. He had written down the page numbers so that he would not forget them. The bill was between pages 45 and 46, he said. But when they looked, there was no money in the book. After Mr. Laidlaw had talked to the cook and the gardener, he called the police. He was sure he knew who had taken the money. Who was it, and how did he know?