"The pen is stronger than the sword."
Translation:펜은 칼보다 강하다.
Saying 강합니다 works grammatically as well, they still seem to be working on having different speech levels accepted as answers
Why is 칼보다 페은 강하다 marked wrong? As far as I know - in this construction the order doesn't matter. This is a feature of both Korean and Japanese
보다 = than copula. The object being compared generally comes before the comparison. Especially since it's a translation of a translation. Order of construction does matter... you'll see how time is usually placed at the beginning of the sentences, how the most important subject is placed closer to the verb, how the verb goes at the end, etc.