Twenty people apply for seven jobs that are available at fly by night aircraft company
In how many ways could such a group be composed?
After the seven have been selected, in how many different ways could five of them be assigned to the assembly department?
number of ways to choose 7 from 20
= C(20,7) = 77520
For each of those, the number of ways you can choose 5 out of the 7 is C(7,5) = 21