! is factorial
it means multipliy all numbers from 1 to that number together
example
1!=1
2!=2*1
3!=3*2*1
etc
some things to note
7!*8=8!
4!*5*6=6!
[tex]\frac{(4!)(7!)}{(6!)(8!)}[/tex]
so we can rewrite it as
[tex]\frac{(4!)(7!)}{(4!)(5)(6)(7!)(8)}[/tex]=
[tex]\frac{1}{(5)(6)(8)}[/tex]=
[tex]\frac{1}{240}[/tex]
