Top Definition
When a tutor uses a fast food premises to teach his student: instead of using his own paper for teaching to avoid being chased away, he uses the outlet's napkins to explain the math concepts.
To use the air con at McDonald's, Jack is a supporter of napkin math: he saves money on renting a room and at the same time his health-unconscious student can order his junk meal there after the tuition is over.
by MathPlus October 04, 2016

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"Napkin math" is the act of performing estimates (usually of a financial nature) to roughly determine the feasibility or validity of an outcome or fact. It is usually performed in an informal setting.

Napkin is an allusion to the disposable nature of the information.
"I've done napkin math Dave, even if you get a $10k/year raise you still can't afford that mortgage".
by silentguardian September 12, 2013

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