Maybe like this?
/ Count(aggr( [Student Number]*[Valid Tariff Count],Faculty,Department, Programme, [Student Number]))
Above is probably not what you want, I missed the part with the not-counting duplicate Student Numbers.
If you rework your data model so that the student number's tariff is a distinct table, I think your version A should match your requirement.
Please check attached.
comm70389.qvw 146.0 K