Since columns can extend beyond pages, the formula might get a little hairy.
Are you wondering the qty per page, or per group?
If by group the formulas below should get you there.
Otherwise, you'd have to know the total lines that can display on the page (printer/font dependent), the height of the group header and footer, etc.
Are you starting separate pages per group and no group will extend beyond a full page? If so, that greatly simplifies the complexity, but it still won't be easy.
Anyway, here's some theory:
This tells you the row count for a group:
Count ({table.Name}, {Table.State})
where {table.name} is the field being counted, {table.State} being the group.
So this gets you 1/2 of that:
int(Count ({table.Name}, {Table.State})/2)
So the next column starts at the above +1.
There's the numbers, hope it helps to get you there.
-k