In a formula field you can put multiple conditions into your IF statement, eg:
IF(
[Field1] = "N/A", [Field2]/5,
[Field1] = "Yes", [Field2]/3,
[Field1] = "No", [Field2]/10,
0
)
Basically this says if the value of Field1 is "N/A" then divide Field2 by 5, otherwise if the value of Field1 is "Yes", then divide Field2 by 3, otherwise if the value of Field1 is "No" then divide Field2 by 10. If all the above are false then make the value 0.
All of these different criteria can be changed to suit your requirements.