How do you find out how many ways the integers

Saniya Copeland

Saniya Copeland

Answered question

2022-06-02

How do you find out how many ways the integers 1,2,3,4,5,6,7,8 can be placed in a circle if: at least three odd numbers are together?

Answer & Explanation

Noemi Flores

Noemi Flores

Beginner2022-06-03Added 2 answers

Step 1
Let's first look at the number of ways we can place three odd numbers together. That's a permutation question:
P n , k = n ! ( n - k ) ! ; n = population , k = picks
P 4 , 3 = 4 ! ( 4 - 3 ) ! = 4 ! 1 ! = 24
Step 2
The rest of the numbers (5) can be placed in any order:
P 5 , 5 = 5 ! ( 5 - 5 ) ! = 5 ! = 120
The one other thing we need to remember is that this is a "sitting in a circle" problem - and so unlike sitting in a row (where there is definitely a chair 1 with person A in it, chair 2 with person B, etc), we have to eliminate the duplicate arrangements from simply rotating the table chairs. Since there are 8 people, there are therefore 8 ways to do each arrangement of chairs, and so we divide by 8.
In total then, we have: 24 × 120 8 = 360

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