to someextent this might help
if attr(customers) = Members and memberid >=300 and memberid <=399
ELSEIF attr(customers)<> Members then sum(amount)
You can do something like:
IF [Customer ID] >= 300 and [Customer ID] <= 399 then 'Member'
ELSE 'Others' END
Drag this calculated field to rows and double click on the value measure from the measures pane!
Thanks a lot for your help and time. I understood the logic and found my mistake. I fixed it using your logic. Thanks again :-)