Why sollen is used in the solution given by duolingo? Should it not be sollten for 'should'. Can anyone explain?
Yes but the solution given by duolingo mentioned sollen. I'm asking it must be sollten (for 'should') right?-- Sie sollten mehr Wörter lernen. Or can you point me out to a link which clearly explains me the function of soll in past and present?
DL's translation is fine (in my opinion at least). But you are right: 'They should learn more words' could be translated with sollte as well. Perhaps it would help to think of sollen as 'to be supposed to'; 'They are/were supposed to learn more words'. The difference is easier to see this way. And in my opinion, it is also a more accurate translation (I am not a native German speaker, though). I have a feeling that the problem here lies in the fact that some English auxiliary verbs are much more irregular than the German ones. My English, however, is far from perfect, so I really should not lecture on English grammar
Bad English translation. I translated it as "they should learn more words" and it was counted correct, but "They are supposed to learn more words" was offered as the duo-lingo approved translation. Nowhere in the German sentence does it say anything remotely related to suppositions or presumptions. It only says that they ought to learn more words.