Questions & Answers about Onko uusi sänky lyhyempi kuin vanha?
How is lyhyempi formed? I know the basic word for "short" is lyhyt.
To add the comparative ending -mpi, you must attach it to the word's vowel stem. For words ending in -ut or -yt (like lyhyt), the stem changes to end in -ue- or -ye-. So the stem of lyhyt becomes lyhye-. Add -mpi to that stem, and you get lyhyempi (shorter).
Why is vanha in its basic dictionary form here?
Because it is part of a kuin (than) comparison. When you use kuin, the two things being compared usually match in their grammatical case. We are comparing the old bed to uusi sänky (new bed), which is in the basic nominative case. Therefore, vanha stays in the nominative case too.
The English translation says "the old one", but the Finnish sentence just ends with vanha. Why isn't there a word for "one"?
Finnish doesn't use a filler word like "one" when an adjective stands alone. If the noun is obvious from the context (like the bed in this sentence), you can simply use the adjective by itself. The sentence literally translates to "Is the new bed shorter than the old?"