Way to divide the values of two custom columns?

I have two calculated custom columns driven by WEEKDAYDIFF expressions and I'd like to divide one by the other:

• one column tells me the number of business days left until the Planned Completion Date
• one column tells me the number of days difference between the Planned Completion Date and the Estimated Completion Date

For each task, I want another column to divide the value in the second column by the value in the first.

Is that possible? Please help!