CountIf with Dynamic Reference

Hey parry2k - 

I'm trying to divide an number by the count of rows with the same reference ID. For example, in the below table the reference ID "ID123" shows up 3 times throughout.

         a              b            c

1     ID123       101

2     ID002       243

3     ID123       101

4     ID123       101

5     ID002       243

6     ID002       243

7     ID002       243

I would like in cell c1 to show 101 / 3. However in cell c2, I would want to see 243 / 4 because the countif will only count rows with an ID that matches the ID in the current row. Hence the cell instead of a hard coded criteria. At least that's how it works in excel. How can I accomplish this in PBI?

Thanks!!