一个由 10 人组成的工作团队包括 7 名男性和 3 名女性,女性的名字分别为 Anne、Beth 和 Cathie。为了即将进行的一次消防演习,将选出 5 人,每人被分配一个唯一的角色来执行演习。确定从这 10 人中选出 5 人的可能方法数:
- (i)
来进行消防演习。
- (ii)
使得最多选出 1 名女性来进行消防演习。
- (iii)
消防演习结束后,这 10 人将在一个有 10 个相同座位的圆桌旁进行讨论。确定 Beth 恰好坐在 Anne 和 Cathie 之间的排座方法数。
- (iv)
讨论结束后,这 10 人排成两排(每排五人)合影。确定 Beth 不与 Anne 或 Cathie 相邻站立的排位方法数。
它不会直接告诉你答案,而是问你卡在哪一步看看 AI 是怎么陪你一步步弄懂这道题的
完整解法
8(i)
1. Calculate the number of ways to choose 5 people out of 10 and assign them to unique roles
\text{Number of ways} = {}^{10}P_5 = 30,240
30,240
8(ii)
1. Calculate the number of ways to choose and assign roles for a team of 0 women (i.e. 5 men)
The condition 'at most 1 woman' splits into two mutually exclusive cases: exactly 0 women and exactly 1 woman.
For 0 women, we select 5 men from the 7 available and arrange them into 5 unique roles:
2. Calculate the number of ways to choose and assign roles for a team of exactly 1 woman and 4 men
For 1 woman, we select 1 woman from 3 and 4 men from 7, then arrange all 5 selected individuals into the 5 unique roles:
3. Sum the cases to find the total number of valid ways
Total number of ways
8(iii)
1. Determine the number of internal arrangements for Anne, Beth, and Cathie.
Since Beth must be seated between Anne and Cathie, the valid arrangements for these three people are Anne-Beth-Cathie and Cathie-Beth-Anne.
Number of ways
2. Calculate the total number of circular arrangements by treating the restricted group as a single unit.
Treat the group of three women as unit. There are remaining men, making a total of units to arrange around the round table.
The number of ways to arrange units in a circle is .
8(iv)
1. Find the total unrestricted number of arrangements for the 10 people.
2. Find the number of arrangements where Beth is standing beside Anne (and similarly for Cathie).
In each row of 5, there are 4 pairs of adjacent positions, giving pairs in total.
Treating Beth and Anne as a block, they can occupy any of these 8 adjacent pairs and can be swapped internally in ways.
The remaining 8 people are arranged in the remaining 8 seats in ways.
Similarly, the number of ways Beth is beside Cathie is also .
3. Find the number of arrangements where Beth is standing beside both Anne and Cathie.
For Beth to be beside both, they must form a 3-person block (Anne-Beth-Cathie or Cathie-Beth-Anne) in the same row.
In each row, there are 3 such blocks of three adjacent positions, giving blocks in total.
Beth must strictly be in the middle, while Anne and Cathie can be swapped in ways.
The remaining 7 people are arranged in the remaining 7 seats in ways.
4. Use the principle of inclusion-exclusion and the complement method to find the required number of arrangements.
Using the principle of inclusion-exclusion, the number of ways Beth is beside either Anne or Cathie is:
Subtracting this from the unrestricted total gives the number of ways Beth is not beside either of them:
AI 分析,可能出错
用 AI 批改,圈出写错的那一步,并自动将你的薄弱点存入错题本,形成你的错因库。
同一知识点的其他题
- 1一项性格测试评估 32 项核心特质。这 32 项特质被分为 4 个领域——认知(Cognition)、影响力(Influence)、人际和谐(Rapport)和规划(Planning),每个领域包含 8 项特质。一个人的测试结果由他/她排名…
- 2一位业余作曲家正在编排一段由四个音符和接下来的三个节拍组成的序列。有 7 种可能的音符(标记为 A 到 G)和 5 种可能的节拍(标记为 1 到 5)。音符和节拍的顺序在创作中很重要。求随机选择的序列满足以下条件的概率: 第三个节拍的数字大…
- 3Alice有24个苹果。她有多少种和Becky与Chris分享苹果的方式,使得三人中的每个人都至少有2个苹果? A. 105 B. 114 C. 190 D. 210 E. 380
- 4Abby, Bridget和其他四个同班同学坐在如下所示的两行三列的座位上准备拍集体照。 如果座位是随机分配的,那么Abby和Bridget坐在同一行或者同一列的相邻位置上的概率是多少? A.…
- 5学校进行羽毛球选拔赛,每个参赛选手都要和其他所有选手赛一场.若有20人参赛,那么一共要进行 场选拔赛.