to get a member value in olap

[cognos05]

I have a dimension called business days and it has members as  1,2..23etc

Now i need to do a revenue perday calc on the report , where i will have my report like below

business day  Sales    MTDSales   RevenuePerDay

1               100           100             100/1
2               200            300           300/2
3               200            500            500/3
4               100            600             600/4
5               500            1100          1100/5


Now i need the calculation of RevenuePerday column , I need to know how to get the denominator ,

the 1,2,3,4, 5 are currentmembers of Business days , how can i use them to get their values 1,2,3,4,5 etcc....


Let me know if this is clear.
Thanks,