A company plans to assign identification numbers to its employees. Each number is to consist of four different digits from 0 to 9, inclusive, except that the first digit cannot be 0. How many different identification numbers are possible? Answer: 4536 But I think, C(9,1)C(9,1)C(8,1)C(7,1).Where am I wrong?
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发表于 2006-7-15 22:56:00
