Get Average of All Displayed Values in Column

Hi,

I want to do something nice in report builder 3.0 (SSRS 2008 R2)  based on a simple t-sql query. below result it's kind of nonsense but this is the requirement.

this example is just to explain the idea. t-sql query  results :

Day Product  AvailableQuantity

1   A 5

1    B10

2    A15

2     B20

Report table should look like :

Product   Max Value

A  15

B  20

Avg  17,5

Basically, I'd like to calculate an average based on displayed values in the report. 

I know how to do this in T-SQL but I really want to gain knowledge about Reporting Services.