Find the number of three-digit numbers possible if only the

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Find the number of three-digit numbers possible if only the digits 0,1,2,3,4and5 may be used,the number must be a multiple of 5,and no digit may be used more than twice in the same number

一个三位数,只能由0,1,2,3,4,5来组成,它必须是5的倍数,这个数中每个数字使用不能超过2次.这样的数有几个?
必须是5的倍数,说明最后一位只能是0或5.
第一位数可以是1-5中任意一个,第二位数可以是0-5中任意一个,第三位数是0或者5.
概率是5 x 6 x 2 = 60
因为每个数不能用两次以上,上面唯一一个例外是555这个数,去掉以后是59个.
所以可以有59个这样的数.

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