Hi Pawan,
There are so many ways,:
One, as you said, you defined this itab as a attribute of this Object, then you need define another attribute 'AverNum' as public. Of cause, this Object have a method using to calculate the average number, passing the value to public attribute 'AverNum', then you can access this public attribute from outside.
Another way: Define this itab as a importing parameter of your average method, same time, this average method have a return parameter. Then you can call this static object method or instance object method from outside, and return your output by return parameter.
regards,
Archer