HMMT 二月 2000 · POW 赛 · 第 2 题
HMMT February 2000 — POW Round — Problem 2
题目详情
- Find the n um b er of 3-letter "w ords" that use letters from the 10-letter set f A; B ; C ; :::; J g in whi h all letters are di eren t and the letters app ear in alphab eti al order.
解析
- 10 9 8 giv e the n um b er of all di eren t 3 letter w ords. One sixth of these are in 10 9 8 alphab eti al order. = 120 . 6