That would make sense if you are assuming that you use the same amount of each ink every time you print a page or set of pages. The black cartridge will probably be used more often.
ok, on the same theme of buying a printer and trying to work out (eventually) the cost per page..
say a toner cartridges average lifespan is 25,000 pages,
and you need a black cartridge and three colour cartridges..
Do I work this out multiplying their lifespans together? Does this make sense?
25,000 pages each, four cartridges = 100,000 pages total?
Am I way off the mark here?
Well, if you print until there is no ink any ANY cartridge then you will get 100,000 pages, assuming of course that you print in ONLY the colours available. For example if you run out of black, and try to print in black... causes problems, etc.
Btw 100,000 is what you get when you ADD the lifespans of the four cartridges, not multiply. Multiplying them gives 390625000000000000.