.
a) around a table where two of them sit beside each other;
2*(9-2)! = 2*7! = 2*5040 = 10080. ANSWER
b) around a table (no restrictions);
(9-1)! = 8! = 40320. ANSWER
c) in a row of 9 chairs.
9! = 362880. ANSWER
---------------
On Permutations, see introductory lessons
- Introduction to Permutations
- PROOF of the formula on the number of Permutations
- Simple and simplest problems on permutations
- Persons sitting around a circular table
in this site.
Also, you have this free of charge online textbook in ALGEBRA-II in this site
- ALGEBRA-II - YOUR ONLINE TEXTBOOK.
The referred lessons are the part of this online textbook under the topic "Combinatorics: Combinations and permutations".
Save the link to this textbook together with its description
Free of charge online textbook in ALGEBRA-II
https://www.algebra.com/algebra/homework/complex/ALGEBRA-II-YOUR-ONLINE-TEXTBOOK.lesson
into your archive and use when it is needed.