function to count the average, check if not empty, then count

Hi,

I'm trying to make a tool for my kid to see the average of his marks.
Like this:

Capture1.JPG

The result are in bold in the table, calculated with the following formula:
=((B22*C22)+(B23*C23))/(C22+C23)
and
=((E22*F22)+(E23*F23))/(F22+F23)

My question is the following: in order to prevent to have to modify the formula everytime I enter a new note, is it possible to ahve it done automatically?
Like the cell is checking that from row 22, if it different than empty, then it starts to count, then the following one and so on till the first row that is empty.

Thanks for your answers!

E

Here is a sample to do it.
I embedded your solution and naturally it works fine.

Only, I was wandering whether it possible to do that without have to "fasten" the array:
Imagine I keep to enter datas, and I go over the array, I have to extend it everytime.
Isn't it possible to have the function check whether the following cell is empty, and if not, the extend automatically the array?


marks sample.xlsx