PUMaC 2009 · 组合（A 组） · 第 3 题
PUMaC 2009 — Combinatorics (Division A) — Problem 3
题目详情
- How many strings of ones and zeroes of length 10 are there such that there is an even number of ones, and no zero follows another zero?
解析
- How many strings of ones and zeroes of length 10 are there such that there are an even number of ones, and no zero follows another zero? Solution. 72. When there are 10 1’s, there is only 1 string; when there are 8 1’s, there are ( ) ( ) 9 7 = 36 strings; when there are 6 1’s, there are = 35 strings. Thus, in total, there are 72 2 4 strings.