Jeremy Siegel says that in finance we should be using geometric and not arithmetic averages.

杰里米·西格尔认为在金融上应该用几何平均,而不是算术平均

耶鲁公开课 - 金融市场课程节选

Not exactly a simple error in arithmetic.

FORBES: Merrill Lynch Settles Customer Suitability Case Despite Apparent Profitability

Of course, what happens in local elections does not (directly at least) change the arithmetic in the House of Commons.

BBC: The year ahead in Parliament

If he does not, then Germany knows that the harsh budget arithmetic in the new Stability and Growth Pact will not add up even for France - let alone the likes of Spain.

BBC: Who will dictate Europe's future?