GMAT数学题求详解
帮忙详解此题，找出答案并解释为什么，一道GMAT数学题 If a code word is defined to be a sequence of different letters chosen from the 10 letters A, B, C, D, E, F, G, H, I, and J, what is the ratio of the number of 5-letter code words to the number of 4-letter code words? A. 5 to 4 B. 3 to 2 C. 2 to 1 D. 5 to 1 E. 6 to 1
答：答： (10!/(10-5)!)/(10!/(10-4)!)=6!/5!=6:1 更直观一些, 就是5位的排列总数比4位排列的总数 每个字母用一次 10×9×8...详情>>
