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HMMT 二月 2000 · GEN 赛 · 第 13 题

HMMT February 2000 — GEN Round — Problem 13

专题
Discrete Math / 离散数学
难度
L3
来源
HMMT

题目详情

  1. Ho w man y p erm utations of 123456 ha v e exa tly one n um b er in the orre t pla e?
解析
  1. The n um b er of rearrangemen ts k eeping 1 n um b er in its sp ot and rearranging the other 5 su h that none are in the righ t sp ot is 44. There are 6 n um b ers to x, this giv es us an answ er of 44 6 = 264 .