"Sie sollen mehr Wörter lernen."

Translation: They are supposed to learn more words.

[Talat]

Here! Here!

[angus390025]

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.

[Drucicha]

can't sollen be translated by "have to"?

[EvelineF.]

Works wrong by me

[Sack11]

Why sollen is used in the solution given by duolingo? Should it not be sollten for 'should'. Can anyone explain?