what I want is to use math in arduino to create a new variable that holds the value of the voltage that I am reading divided by 5 and then output to serial.
Are you asking for permission? If so, it's granted.
If not, then surely you know how to define a variable. After all, you had to do that to hold the value read from the pin. So, create another one. Dividing by 5 is a no-brainer.