And on many occasions, it was on the back of an envelope or on a napkin that she doodled sketches of the chemical bonds to better show her parents what she was working on in the lab.

以前的很多时候，她就是通过在信封或者餐巾纸的背面画化学键的草图，向父母解释她在实验室里的工作。

youdao

I dated this one American guy who was so miserly that at the end of the evening he would tot up on the back of his napkin what I owed him down to the last cent.

我约会的那个美国人竟如此吝啬，晚上约会结束时他都会在纸巾背面计算我用了他 多少 钱，细到 一个美分都不放过。

youdao

And the calculations are not easily done on the back of a napkin.

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"I'd like to buy the world a Coke and keep it company, " Backer wrote on the back of a napkin.

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And that number--published by the New York tabloids--is little more than an educated guess made on the back of a napkin.

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