Question

How many ways can 5 sopranos and 4 altos be selected from 7 sopranos and 9 altos?

Answer 1

They can be selected in 2646 ways.

$_7C_5\times_9C_4=\frac{7!}{5!2!}\times\frac{9!}{4!5!}=21\times126=2646$