GRE
The total number of positive 4-digit integers that can be formed where each digit is in set T and the 4 digits in each 4-digit integer are different from each other
(7)(6)(5)(4)
$$\sqrt{( 10^{2m} )( 10^{2n} )}$$
$$10^{mn}$$
25000 +道题目
236本备考书籍