OS X Numbers: How to use a spreadsheet value as a label
As far as I can see, chart titles and labels (and text boxes) can't contain formulae.  So I think this isn't possible in the ways that you suggest.

An alternative is to place a single-cell table on top of the chart, with the cell containing a formula like = "Salaries normalised to " &amp; B1 &amp; " school days".



I'm using Numbers '09... hopefully this still works in later versions...