How to include a Dynamic cell reference in a Fomula?

[michael tay]

Col1 Col2
23 3
4 44
43
33

Assuming the data above.
Since different columns have different lengths, I need to calculate the
length for each column separately.

At the last row. I need to enter formula to calculate the average for each
column,
how do I do something like formula = "average( Range(cells(2,1), cells(2,
lastrow))) "

where lastrow can be dynamically changed.

Thanks.