Questions & Answers about Ég þarf að kaupa annan púða og aðra mottu.
Why does another translate to annan for the cushion, but aðra for the rug?
The word annar changes to match the gender, number, and case of the noun it describes. The verb kaupa (to buy) puts the things being bought into the accusative case. Púði (cushion) is masculine, so it takes the masculine accusative form annan. Motta (rug) is feminine, so it takes the feminine accusative form aðra.
Why do the nouns end in -a and -u here?
Both púði (cushion) and motta (rug) are in the accusative case because they are the objects being bought. Púði is a weak masculine noun, which means its ending changes from -i to -a in the accusative. Motta is a weak feminine noun, which changes from -a to -u.
Does annar mean an additional one or a different one in this sentence?
It can mean either, just like another in English. Depending on the situation, the speaker might want a second cushion to match one they already have, or they might want to replace a cushion with a totally different one.
Why is there an að before kaupa?
The verb þurfa (to need) links to other verbs using að plus the infinitive form of the action word. So ég þarf að kaupa translates directly to I need to buy.