back-of-the-envelope

昨日投稿したback up the Brink’s Truckを調べている最中に見つけた記事から英語表現を拾います。記事はメジャーリーグアメリカンリーグに属するOakland Athleticsのホームページからの引用です。
今回採り上げるのはback-of-the-envelope math。これはイメージしやすい表現ですが，封筒の裏に書いてできる計算から「簡単な計算、大雑把な見積もり」と解釈できます。同様の意味でback-of-the-envelope calculation（英辞郎 on the WEB）という言い方もあるので合わせて押さえておきましょう。（Koyamamoto）

Back Up the Brink's Truck for Jorge Soler
By my back-of-the-envelope math, the A's just saved $10-15MM for this upcoming season by trading away Trevor Cahill, Gio Gonzalez, and Andrew Bailey. Even after figuring in a handful of arbitration raises and league-minimum salaries for the new guys, the A's are looking at a rather nice amount of cash on their hands. The savings over the next few years will be even greater, considering that Gonzalez and Bailey are going into their first year of arbitration, and that Cahill has only cashed in $500,000 of his $30.5MM contract. We don't know much about the Athletics' financial books, but considering that they offered a rumored $64MM deal to Adrian Beltre last winter, they clearly have a little spending money.
http://www.athleticsnation.com/2012/1/3/2675317/back-up-the-brinks-truck-for-jorge-soler