thx for your reply. with the particular numbers I gave it comes out as eur/aud vol is 8.72
just thinking, this isn't a no arbitrage type figure though, right? because vol itself is traded so eur/aud vol could really be anything? if it doesnt follow the mathematical relationship (i.e. related in a particular way to the vols of the first two pairs), wouldn't there be arbitrage opportunities?
curious for thoughts.