SumDistinct in report builder 2

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SQL-Server-2005

SQL

SQL-Server

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Dear,

I am building a report using report builder 2.
let say the data from my query is look like below:

Select membershipid,billamount,transactionAmount
From  membership m inner join bill b on b.membershipid=m.id
left outer join transaction t on t.billId=b.id

MembershipId(membership Table) billAmount(bill)  TransactionAmount (transaction)
1                              100                   20
1                              100                   20
1                              100                   50
1                              100                   10
2                              50                    10
2                              50                    10 
2                              50                    20

when I used the row group in report builder on membershipId then add Total group
,report output is like this:

1                             400                  100
2                             150                  50

I want to see this output:

1                             100                  100
2                             50                   50

why this happen?and What should I do؟