Roughly speaking = approximately, lacking precision.
In a nutshell = concisely, using few words.
2018年11月3日
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"Roughly speaking" means "speaking generally" - used for giving information that is general and not exact.
- Roughly speaking, it'll take eight days.
"In a nutshell" can mean either "in summary" or "in brief"
- In a nutshell, it can't be done!