http://finance.yahoo.com/q/is?s=AAPL&annualgenerik said:1) Eh.. $p by definition would be the pure gravy.. stuff like advertising and administration would fall under $c.
Using you definition Apple's net profit margin was ~12% for the last year reported here (2005), i.e. nowhere near 20%. Using the more typical definitions they're operating with 29% gross margin accross the board. Which is pretty typical. G&A expenses were similar to the net profit (again typical) and R&D was less (~5%). Pretty typical.
http://finance.yahoo.com/q/is?s=DELL&annual
Dell's most recent profit margins accross the board were 18% gross and 8% net with 9% G&A and under 1% R&D.
These differences are consistent with the two companies differing business models. Dell does no R&D, and thus can't expect to command the extra 4% profit margin.
B