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
Question 10
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:
(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)=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!=120 ways.
Thus, the total arrangements will be:
2(teachers)×6(gaps)×120(students)=1440.
Step 4
Conclusion
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Answer
Altogether, considering all combinations and arrangements, the final answer is: