There are 7 non-national competitors and 2 open slots for them, so find the number of combinations for that, which is 21.Originally Posted by Stuart
Now there are 3 national competitors and 2 open slots, the number of combinations for that is 3.
For each combination of national competitors there are 21 combinations of non-nationals, so 3*21.
3*21 is 63
so there are 63 possible relay teams.