1. Open up the Field Explorer:
    In Crystal 8.5 - select Insert/Field Object
    In Crystal 11 - select View/Field Explorer

2. Right click on "Formula Fields" and select "New" and give this formula an appropriate name to represent the result of the division and select OK.  This will bring up the Formula Editor/Workshop.

3. You should see at the top of the Formula Editor/workshop a section for "Report Fields", a section for "Operators" and a section for "Function".  Below the "Report Fields" entry you will see the "location/path" of your current Data file.  Select the "+" next to Location/Path of current data file.  Locate the Table/field that represents the field you wish to use in the Numerator and then double click on this field.  Locate the Table/field that represents the field you wish to use in the Denominator and then double click on this field.  Now both fields are in the bottom window of the Formula Editor/workshop.

4. Place a divide symbol "/" between the two fields so that your formula looks like the following:
 {'Numerator_Field'} / {'Denominator_Field'}

This should give you the result you want.  If it gives you an error instead, please check the following:

a. Make sure that the fields you selected are number fields and not a string fields.  If either or both are a String fields you can use the Val function to change this.  Below is what you would use if both are string fields.

Val({'Numerator_Field'}) / Val({'Denominator_Field'})

b. Make sure you aren't getting any Zero values in the {'Denominator_Field'}.  You can get around this by the following:

If {'Denominator_Field'} <> 0 then
   {'Numerator_Field'} / {'Denominator_Field'}