There can be 7 groups that can be created with no one left out.
boys = 14
girls = 21
We need to find the factors of each number.
14: 21:
1 x 14 1 x 21
2 x 7 3 x 7
Both have the same factor of 7. So there can be a maximum of 7 groups with 2 boys and 3 girls per group.