Calculate percentage of total sales

Calculate percentage of total sales

Hi,
I am kind of new in Zoho reports, so I will need your support...
I would like to know for each client what is the percentage of sales.
I am familiar with formulas and aggregated formulas but i didn't manage to make it works.
Tnx
L

Client

Jul 2012

Oct 2012

Nov 2012

Total by client

Percentage of total sales

Client 1

 $    4.00

 $          4.00

4/52  = 7.69%

Client 2

 $    4.00

 $  21.00

 $  23.00

 $         48.00

48/52= 92.31%

Total

$         52.00

100.00%