Peter:

I basically agree with Scott's analysis (except I don't understand why
he divided by three if he's putting 4 spreads on a sheet),




Scott:

At four spreads per sheet you'd need 51 ÷ 3 = 17 sheets per copy.




I meant "At three spreads per sheet..."

Peter (again):

reducing the size of the page will increase the number of sheets required.

That will be true if reducing the page size actually both increases the
page count and leaves the number of pages per sheet the same, but those
are two large assumptions.




I didn't assume anything. I presented a scenario where that's exactly what happened.