I have just seen these two sentences:
“Einige Mitarbeiter sind hier nicht glucklich”
“Manche Menschen haben einen sechsten Sinn”
I know that “einige” and “manche” in both sentences mean “some”.
Am I 100% correct if I say that both words are interchangeable?

Apparently manche and einige are not quite the same, but the difference is subtle.
You will find a discussion here:
https://forum.wordreference.com/threads/einige-vs-manche.2222759/

Hi there,
I have been studying the words plus “Etwas”.
I think I have a good understanding of the words, but I would like to be 100% sure.

Manche:
As a pronoun it only exists in plural form
Can be used for both countable and uncountable things
Used when referring to something of a very small amount e.g. 2-3 out of a 100

Einige:
As a pronoun it only exists in plural form
Can be used for both countable and uncountable things
Used when referring to something of a noticeable amount e.g. 20-30 out of 100

Etwas:
As a pronoun it only exists in singular form
Only  used which something which is uncountable
 
1. Is my understanding correct?
 
2. As I see it “Etwas” can sometimes be interchangeable with “Einige” and “Manche”. Is there a clear cut of when “Etwas” should be used instead?

Hi RexV, 

Manche: 
Everything sounds correct, except it referring to a "very small amount". I would rather call it "a small, but noticeable amount" (less than einige).

Einige: Everything is correct.

Etwas: It can be interchangeable with einige und manche, but if it's associated with an uncountable word, you would always rather go for etwas. In fact, if you want to be on the safe side, use einige und manche only for countable words and etwas for uncountable ones.

I hope this helps. 

Liebe Grüße, 
Leah von Rocket German

Super!

I guess a good example with "etwas" could be "Ich möchte gerne etwas Wasser trinken"?

Best,
Rex

Hallo Rex,

Yes, that's a perfect example of the use of etwas!

Tschüss,

Liss