The notes were always on scratch paper or the back of an envelope, nothing fancy.

这些笔记总是在便笺或信封背面上，没什么特别的。

《柯林斯英汉双解大词典》

Don't write the address on the back of an envelope.

不要把地址写在信封反面。

youdao

I make some rough calculation in the back of an envelope.

我在信封的背面做了一个粗略的估算。

youdao

I make some rough calculation in the back of an envelope.

我在信封的背面做了一个粗略的估算。

youdao