Adding in a calculated column - percentage

Percentage%=DIVIDE([# Classes Canged],[# ALL classes],0)

Hi!
If # Classes Changed and # All Classes are from different tables you can use LOOKUPVALUE() first.

You need some sort of common key for each class in your tables (called ClassKey below, change accordingly). This also assumes that you create the columns in your table with the All Classes (ACTable) value and not the table with Classes Changed (CC Table). You can do it the other way around, but need to switch up the DAX then.

Then a calculated column should be able to look something like this:

% changed =
VAR __CurrentClass = 
ACTable[ClassKey]

VAR __ClassesChanged = 
LOOKUPVALUE(CCTable['# Classes Changed'],CCTable[ClassKey], __CurrentClass)
VAR _

return

DIVIDE(
    __ClassesChanged,
    ACTable['# All Classes'])

Good luck!

I should have noted that '#Classes changed' and '#All classes' are from two different tables. 

Another easy way, if you don't need it to be a calculated column and are ok with a measure (that can be shown as a column in a matrix) could just be to calculate the sum for each and then divide them:

Percentage :=
DIVIDE(
    SUM([# Classes Changed]),
    SUM([# All Classes])
)

It might depend on how your data is structured, but a possiblity.