In how many ways can 15 people be seated around two round tables with seating capacities of 7 and 8 people?
In how many ways can 15 people be seated around two round tables with seating capacities of 7 and 8 people?
Solution
When people sit around a round table, rotations look the same. If everyone shifts one seat clockwise, it's still the same arrangement. For people at a round table, there are arrangements (not ).
First, decide which people sit at which table: 7 people go to the 7-seater table and 8 people go to the 8-seater table.
Number of ways to choose 7 people from 15:
For the round table with 7 people, the number of arrangements is:
For the round table with 8 people, the number of arrangements is:
Total number of ways:
Therefore, the answer is
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