So when does the price and the usefulness equation stop people wanting Photoshop at all?

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Add the all-important price of oil to the equation and it begins to look like a time bomb.

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The price of corn is pivotal in the world food equation, and food markets are on edge because U.S. corn stocks are plummeting.

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The price of corn is a critical variable in the world food equation, and food markets are on edge because U.S. corn stocks are plummeting due to the ethanol mandate.

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But the more interesting side of the equation is how Google can make its gigabit price so low.

FORBES: The Economics Of The Google Gigabit

Another experiment revealed that even when price was removed from the equation, participants still went for larger portions.

FORBES: Consumers Opt For Larger Food Portions To Increase Social Status

Or, to turn the equation around: How large a band do you have to draw around today's price to have a certain likelihood (say, 95%) of including tomorrow's price?

FORBES: Magazine Article

The Black-Scholes equation, brainchild of economists Fischer Black and Myron Scholes, provided a rational way to price a financial contract when it still had time to run.

FORBES: Black-Scholes Didn't Cause the Financial Crash