we know that
The formula for combinations is
[tex] C=n!/((n-r)!*r!)[/tex]
where
n is the total number of objects you choose from
r is the number that you choose to arrange
in this problem
[tex] n=20\\ r=4 [/tex]
[tex] C=20!/[(20-4)!*4!]\\ C=20!/[(16)!*4!]\\ C=4,845 [/tex]
therefore
the answer is
[tex] 4,845 [/tex]
