Calculating a value that is not a number

[dreeves]

I have a field with a list box with three values to input in a record. The
row source type in properties is Value List and the Row Source list is "Yes",
"No", and "N/A". Example: I need to count how many "No" and divide that
number in the total number of the field to get a "No" percertage.

 

[KARL DEWEY]

This will do what you want ---
Sum(IIF([Source] = "No", 1, 0))/ Count([Source])

but it may need more depending on where you will be using it.