SOLUTION TO LAST MONTH'S QUIZ
1. 15
2. 105
3. 654729075
Notes
(Notice that the question asks for the number of ways in which all the players can be paired off, not the number of ways of selecting one pair.)
1. A's partner can be chosen in 5 ways.
Then remaining 4 people can be paired in 3 ways (as explained in the question).
So total no. of pairings = 5 * 3
2. A's partner can be chosen in 7 ways.
Then remaining 6 people can be paired in 5 * 3 ways.
So total no. of pairings = 7 * 5 * 3
3. And so on ......
So total no. of pairings = 19 * 17 * 15 * 13 * 11 * 9 * 7 * 5 * 3
