I have a column which, in every 50 rows has a value set, different than the
next set.

For example, in rows 1-50, the value 1.1
In rows 51-100, I have in each row 1.2., etc. etc.

Is there a way I can delete the first 20 of the 50 rows in every set of
values. I'm to keep only the remaining thirty, then delete the following
twenty, and keep the following thirty rows, and repeat the process for the
entire column?

I'm new to all this excel though trying to get better. Any ideas?