As mentioned in the comments, fast = almost, close to (but not same as) Ref.: http://dict.leo.org/englisch-deutsch/fast etwa = approximately, roughly synonyms: circa, ungefähr Ref.: http://dict.leo.org/englisch-deutsch/etwa === Ich wünsche Dir einen schönen Tag.／I wish you a good day.

Ich danke Dir sehr, dass Du dieses Mal meine Antwort wie die beste Antwort gewälht hast. Bitte mach mit der guten Arbeit weiter. Schönen Tag.／Thank you very much for having chosen my answer as the best answer this time. Please keep up the good work. Good day.

yes thank you Lilli ((:

No, they don't mean the same thing. fast = almost - slightly less, not quite etwa = approximately - similar, could be slightly less or slightly more For example, imagine a race between Person A and Person B. If I tell you: "Person A war fast so schnell wie Person B." (="Person A was almost as fast as Person B"), then you know for sure that Person B was faster and won. If I say: "Person A war etwa so schnell wie Person B." (="Person A was about / approximately as fast as Person B) then you know it was a close race, but you don't know who actually won. Does that make sense?

then they can be used instead of eachother?