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A group with 5 students and 3 teachers is to be arranged in a circle - HSC - SSCE Mathematics Extension 1 - Question 10 - 2023 - Paper 1

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A group with 5 students and 3 teachers is to be arranged in a circle. In how many ways can this be done if no more than 2 students can sit together?

Worked Solution & Example Answer:A group with 5 students and 3 teachers is to be arranged in a circle - HSC - SSCE Mathematics Extension 1 - Question 10 - 2023 - Paper 1

Step 1

Step 1: Grouping Students into Allowable Arrangements

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Answer

To ensure that no more than 2 students sit together, we can first arrange the teachers and then insert the students.

When arranging the 3 teachers in a circle, the arrangement can be calculated as:

(31)!=2!=2(3 - 1)! = 2! = 2 ways.

Step 2

Step 2: Inserting Students in Groups

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Answer

To insert the students, we will consider the arrangement of the 3 teachers creating 3 gaps for students (between each pair of teachers) and one gap at the end. This gives us a total of 4 gaps.

We need to choose gaps to place the students while ensuring no more than 2 can sit together. The possible combinations of inserting students in the gaps include:

  • 2 students in one gap and 1 student in each of the remaining gaps.
  • This leads to choosing 2 gaps out of the 4 to hold the students, calculated as:

C(4,2)=6C(4, 2) = 6 combinations.

Step 3

Step 3: Arranging the Students

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After choosing which gaps will contain the students, we can arrange the 5 students in those selected positions. This is done by permuting the students:

5!=1205! = 120 ways.

Thus, the total arrangements will be:

2(teachers)×6(gaps)×120(students)=14402 (teachers) \times 6 (gaps) \times 120 (students) = 1440.

Step 4

Conclusion

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Answer

Altogether, considering all combinations and arrangements, the final answer is:

The answer would match option B: 5! \times 3!.

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