要从5名女性和6名男性中选出一个由六人组成的委员会。其中三名女性是姐妹。在以下情况下,求可以组成委员会的方法数: 所选委员会由两名特定的姐妹、另外3名男性和另外1名女性组成。他们坐在一个专供六人使用的圆桌旁。在以下情况下,求可能的排列数:

  1. ((i))

    所选委员会恰好包含两名男性,

  2. ((ii))

    至少包含姐妹中的一人。

  3. ((iii))

    其中一名男性要坐在两姐妹之间,

  4. ((iv))

    两姐妹直接面对面而坐。

先不看答案,让 AI 诊断你卡在哪里?

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. Identify the number of women needed for the committee

To form a committee of 66 people with exactly 22 men, the number of women required is 6−2=46 - 2 = 4.

2. Calculate the total number of ways to form the committee

Number of ways to choose 22 men out of 66 and 44 women out of 55:
6C2×5C4=15×5=75^6C_2 \times ^5C_4 = 15 \times 5 = 75

答案

7575

6((ii))

1. Calculate the total number of ways to form the committee without restrictions

Total number of people = 5 women+6 men=115 \text{ women} + 6 \text{ men} = 11
Total unrestricted ways to choose 6 people = (116)=462\binom{11}{6} = 462

2. Calculate the number of ways to form the committee without including any of the sisters

Number of people who are not sisters = 11−3=811 - 3 = 8
Ways to choose a committee of 6 entirely from these 8 people = (86)=28\binom{8}{6} = 28

3. Subtract the ways without sisters from the total ways to find the number of ways with at least one sister

\text{Ways with at least one sister} = 462 - 28 = 434

答案

434

6((iii))

1. Find the number of ways to arrange the two sisters and the man between them into a single block.

We choose 11 man out of the 33 available men on the committee to sit between the sisters: (31)=3\binom{3}{1} = 3 ways.

The two sisters can swap places on either side of the chosen man in 2!=22! = 2 ways.

Treating the two sisters and this chosen man as a single block, there are 3×2=63 \times 2 = 6 ways to form this block.

2. Calculate the total number of circular arrangements for all entities.

We now arrange this block along with the remaining 33 people (22 men and 11 woman) around the round table.

Total number of entities to arrange =1 (block)+3 (individuals)=4= 1 \text{ (block)} + 3 \text{ (individuals)} = 4 entities.

The number of ways to arrange 44 entities in a circle is (4−1)!=3!=6(4 - 1)! = 3! = 6 ways.

Total possible arrangements =6×6=36= 6 \times 6 = 36.

答案

36

6((iv))

1. Place the two sisters at the round table.

In a circular arrangement, fixing the position of one person removes the rotational symmetry, leaving 11 way to seat the first sister.
Since the two sisters must sit directly opposite each other, the second sister has only 11 available seat (directly across from the first).
Number of ways to seat the sisters = 1×1=11 \times 1 = 1.

2. Arrange the remaining committee members in the remaining seats.

The remaining 44 members (the 33 men and 11 other woman) can be arranged in the remaining 44 distinct seats in 4!4! ways.
Total number of possible arrangements = 1×4!=241 \times 4! = 24.

答案

2424

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. 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. 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…
  3. 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
  4. 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。 X X XX\ X\ X X X XX\ X\ X 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. 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.