Translation:The man puts the plates on the table.
Can I also omit "πάνω" in this sentence or have i to use it absolutely and if yes - why?
Yes, you can omit it. It was not accepted because we did not think about it, but it is now. ;)
I wrote 'The man puts the plates onto the table' which was marked wrong but it is actually correct English
The duplication led me to a more emphatic translation, viz, "on top of " but this was marked wrong...
I am sorry but how does it expect me to know what "πάνω στο τραπέζι" means? None of these words occured before.
I think that is how Duolingo works. The first time you see a word you either tap it / click on it to see possible translations, or just plan on getting it wrong. Expect to get it wrong several times as you learn it: not a problem! This simply instructs Duo to review the word more frequently for awhile -- which is what you want for a new word! It's a Good Thing. :-)
Also, funny how much τραπέζι is like τράπεζα, bank. I wonder if they're related.
They are. Originally the represantative of a bank and a customer were sitting by a table.
They are, in fact! From what I understand τραπέζι is an abbreviation of τραπέζιον, the diminutive of τράπεζα. While τραπέζι retained the meaning of 'table', τράπεζα has come to mean 'bank'. The maths term 'trapezium' also comes from τραπέζιον!
Another fun fact. Τράπεζα literally means 'three feet', because ancient Greek tables used to be made with three feet. =D
Agree with many above that "onto the table" should be correct - in many dialects of English using "on" rather than "onto" for destination is considered wrong grammar.
When would I have been introduced to the word στο ? I feel I may be missing some links to tips.