Exam Item Analysis

rquizon09 , Try using below steps

First, sort your data by the Score column in descending order.

Create a calculated column to rank the scores. You can use the RANKX function for this.
Rank = RANKX(ALL('YourTable'), 'YourTable'[Score], , DESC, DENSE)

Filter Top N and Bottom N:

TopN_Sum =
CALCULATE(
SUM('YourTable'[Item No.1]),
FILTER(
'YourTable',
'YourTable'[Rank] <= N // Replace N with the number of top scores you want
)
)

Combine the Measures:
Create a final measure to sum the values from the top N and bottom N.
Total_Sum = [TopN_Sum] + [BottomN_Sum]
Add a card or any other visual to display the Total_Sum measure.

Hi bhanu_gautam 

Thank you for your feedback.
I have question on calculated column, I want to rank them based on the subject.

For example.

Subject 1 Rank 1

Subject 1 Rank 2

Subject 1 Rank 3
Subject 2 Rank 1

Subject 2 Rank 2
Subject 3 Rank 1

etc.

Thank you

rquizon09 , You can use the RANKX function along with the EARLIER function to achieve this.

Rank =
RANKX(
FILTER(
'YourTable',
'YourTable'[Subject] = EARLIER('YourTable'[Subject])
),
'YourTable'[Score],
,
DESC,
DENSE
)

Then 

You can create measures to calculate the sum of the top N and bottom N scores.

TopN_Sum =
CALCULATE(
SUM('YourTable'[Item No.1]),
FILTER(
'YourTable',
'YourTable'[Rank] <= N // Replace N with the number of top scores you want
)
)

BottomN_Sum =
CALCULATE(
SUM('YourTable'[Item No.1]),
FILTER(
'YourTable',
'YourTable'[Rank] > (MAXX(ALL('YourTable'), 'YourTable'[Rank]) - N) // Replace N with the number of bottom scores you want
)
)

Hi bhanu_gautam 

Regarding on the calculated column, the formula is not functioning or Am I not execute it properly?

Hi bhanu_gautam 
I want to get the unique rank per subject even though the student scores are duplicated

Hi bhanu_gautam 
I already get the unique ranking every row.
I want to SUM now the Item No.1 based on the Ranking. but the problem is the ranking is equal to 27% of the total count rows per subject. Meaning, the count or ranking will be dynamic.

Thank you

Hi Anonymous 
The Unique Ranking is already solved.
I just want to clarify this formula 

BottomN_Sum =
CALCULATE(
SUM('YourTable'[Item No.1]),
FILTER(
'YourTable',
'YourTable'[Rank] > (MAXX(ALL('YourTable'), 'YourTable'[Rank]) - N) // Replace N with the number of bottom scores you want
)
)

Because this formula does not functioning.

I already have Unique Ranking of Row but I want is to Sum the TopN and BottomN based on Ranking Column.

Thank you