Weighted average calculation in difference set of data

Hi Expert,

I am trying to calculate the weighted average

Here is the raw data
table1.JPG

By using sumproduct function, i can get the weighted average of marks :
result.JPG

But I need to change the range manually, and if the data set is not in ascending/descending order, I cannot even manually change the range to calculate the weighted average.
Data set like :
table2.JPG

Attached please find the excel also.

Please help to advice the formula in cell K3 to K8, if using the the data set of table 2

Thanks!!

Regards,
Chocobo