HMMT 二月 2000 · POW 赛 · 第 7 题
HMMT February 2000 — POW Round — Problem 7
题目详情
- Find the n um b er of om binations of length k that use elemen ts from a giv en set of n distin t elemen ts, allo wing rep etition and with no missing elemen ts. (Ob viously , k m ust b e greater than n )
解析
- W e an use the same metho d as the ab o v e argumen t, ex ept that w e kno w ev ery elemen t o urs at least on e. So, this is the same as ho osing k n times from the n distin t k n n +1 k 1 k 1 ob je ts, so the answ er is , or or . n 1 n 1 k n 62 971