Use parameters to create conditional columns

hi Anonymous 

You could try this as below:

Step1:

Use What if parameter to create a dynamic value for "65"

https://docs.microsoft.com/en-us/power-bi/desktop-what-if

Step2:

Create a simple Grades table that only contains Grade column

Step3:

Then use adjust the formula that  Ashish_Mathur provided.

Measure = VAR _table =
     ADDCOLUMNS (
        Grades,
        "Lower", IF ( Grades[Grade] = "B", [Parameter Value],  SUM(Data[Marks])),
        "Upper", IF ( Grades[Grade] = "B", 0, [Parameter Value] )
    )
RETURN

COUNTROWS (
    FILTER (
        ADDCOLUMNS (
            VALUES ( Data[Student] ),
            "XYZ", CALCULATE (
                [Scores],
                CALCULATETABLE ( VALUES ( Data[Student] ) ),
                ALLSELECTED ()
            )
        ),
        COUNTROWS (
            FILTER ( _table, [Scores]>=[Upper]&&[Scores]<=[Lower] )
        ) > 0
    )
)

here is sample pbix file, please try it.

Regards,

Lin