在卡里斯马初级学院(Charisma Junior College)的学生会中,共有 31 名成员,其中包括学生服务(SS)部门的 22 名成员和魅力影响力(CI)部门的 9 名成员。在学院的晨会上,共有 6 名成员值日,两人一组进行。 每天早晨的三项不同值日任务包括:每日启示(Daily Inspirations)、升旗(Flag Raising)以及领唱国歌和领读誓词(Recital of the national anthem and pledge)。除了“每日启示”部分必须由 CI 部门的成员执行外,所有值日任务都可以由任何学生会成员执行。求:
- (i)
所有可能的值日分组总数。
- (ii)
CI 部门成员 Jill 参与值日的值日分组总数。
- (iii)
SS 部门成员 Jack 参与值日的值日分组总数。
- (iv)
由此说明如果第 (i) 部分中的值日分组是随机抽取的,这对学生会成员是否公平,并给出理由。
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
6(i)
1. Find the number of ways to assign members to the Daily Inspirations duty.
The Daily Inspirations duty requires 2 members, both of whom must be from the CI Wing (which has 9 members).
Number of ways =
2. Find the number of ways to assign the remaining members to the other two distinct duties and calculate the total.
The remaining two duties (Flag Raising and Recital) are distinct and require 2 members each. There are no restrictions, so we choose from the remaining members.
Number of ways for Flag Raising =
Number of ways for Recital =
Total number of possible duty groupings =
6(ii)
1. Calculate the total number of possible duty groupings (using the result from part i).
To find the total unrestricted groupings, we choose 2 members from the 9 CI members for Daily Inspirations (DI). Then, from the remaining 29 members (31 total - 2 chosen for DI), we choose 2 for Flag Raising (FR). Finally, from the remaining 27 members, we choose 2 for Recital (R).
2. Calculate the number of duty groupings where Jill is NOT on duty.
If Jill is entirely excluded from the morning duties, we remove her from the available pool. The CI Wing now has members, and the overall available pool (excluding Jill) is members.
We choose 2 for DI from the remaining 8 CI members:
The remaining available pool is now members. We choose 2 for FR:
The remaining pool is members. We choose 2 for Recital:
3. Subtract the groupings without Jill from the total groupings to find the answer.
Using the complement method, the number of groupings where Jill is on duty is the total possible groupings minus the groupings where she is excluded:
1,690,416
6(iii)
1. Establish Jack's possible duties and calculate the ways to assign the Daily Inspirations (DI) duty.
Since Jack is in the SS Wing, he cannot be assigned to the Daily Inspirations (DI) duty (which is restricted to CI members). He must therefore be assigned to either the Flag Raising (FR) or the Recital (R) duty.
The DI duty must first be filled by 2 members chosen from the 9 in the CI Wing:
2. Assign Jack to a duty, choose his partner, and assign the remaining duty to find the total combinations.
Jack can be assigned to either the FR or R duty ( choices).
Once his duty is chosen, he needs partner from the remaining members (since are in DI and Jack is , leaving ): .
The remaining duty requires members from the members left: .
Using the multiplication principle:
707,616
6(iv)
1. Establish the values from the earlier parts to compare the number of groupings for a CI member versus an SS member.
Total possible duty groupings (from part i):
Groupings where Jill, a CI member, is on duty (from part ii), found by subtracting groupings without her:
Groupings where Jack, an SS member, is on duty (from part iii), found by subtracting groupings without him:
2. Compare the number of groupings to justify the comment on fairness.
Since , a CI member is involved in more than double the possible duty groupings compared to an SS member. If a grouping is picked uniformly at random, a CI member inherently has a higher probability of being chosen for duty. Thus, the system is not fair.
It is not fair. A member of the CI Wing (like Jill) appears in possible groupings, whereas a member of the SS Wing (like Jack) appears in only possible groupings. Since a CI member has a significantly higher chance of being picked than an SS member, picking groupings at random is unfair.
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.