Doing the Math on a Napkin
ist in Bayern "Berechnungen auf dem Bierdeckel erstellen". This is not a literal translation but an adaptation - the content of the message is being adapted to the locale, or region. The value of the message remains the same by changing it.
The technique of adaptation vs translation is common in marketing and advertising, where conveying an emotional value or a punchline supercedes the requirement to have text translated close to the original.
Doing the Math - has a certain connotation in America - often it is used slightly ironical, where an unsuspecting person finally gets to do the math and figures things out. So doing the math often has to do with numbers but not always. Oh, this is another good one - to figure things out [ to figure - calculate, to work out | to figure out - to unravel]. To figure things out is to come to understand a situation or issue that is complicated or convoluted, not quite obvious, or even concealed by design.
Take Courtney Love, a real life example: according to blogger Mary Hodder graduate student at UC Berkeley's School of Information Management and Systems, Courtney finally does the math when she figures that bosses of record companies steal from her more than . . .
Another, fictional, example:
Hank came up with this great-sounding business plan, but Jill sat him down and made him do the math. Then things didn't look so great.
Hank kam mit diesem Geschäftsplan an, der ziemlich großartig klang. Jill sagte
- Nun setz dich mal hin und rechne das mal ordentlich nach.
Daraufhin sah das alles nicht mehr ganz so großartig aus.