标题: 问道prep ps1，算不出选项的答案 [打印本页] 作者: newport 时间: 2010-9-13 12:40 标题: 问道prep ps1，算不出选项的答案 39. 5583-!-item-!-187;#058&004668 A certain stock exchange designates each stock with a one-, two-, or three-letter code, where each letter is selected from the 26 letters of the alphabet. If the letters may be repeated and if the same letters used in a different order constitute a different code, how many different stocks is it possible to uniquely designate with these codes?
(A) 2,951 (B) 8,125 (C) 15,600 (D) 16,302 (E) 18,278 ------------------------------------------------------------------------------------------------------------------------------------ 【答案】E 【思路】題目有前提If the letters may be repeated and if the same letters used in a different order constitute a different code, 所以one letter-26種 two letters-26x26種 three letters-26x26x26種 total=18,278 ----------------------------------------------- 26^3 =17576,??