Hello Altshaka!
Total subcommittees = Seventh Grade Group * Eighth Grade Group
Seventh Grade Group = choosing 3 seventh graders out of 10.
\({10 \choose 3}=\frac{10!}{7!3!}=120\)
Eigth Grade Group = choosing 3 eighth graders out of 8
\({8 \choose 3}=\frac{8!}{5!3!}=56\)
Total subcomittees = 120 * 56 = 6720
- I'm not so sure if this is correct, but this is my attempt on the problem.