There are two ribbons, respectively 42cm and 30cm long. If they are to be cut into short colored ribbons of the same length without any surplus, how many centimeters can each ribbon be at the longest?
有两根彩带，分别长42cm和30cm．要把它们截成同样长的短彩带且没有剩余，每根彩带最长能有多少厘米？
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