Learn Swedish: Vi tror inte det.

In Swedish, tror is used for both "believe" and "think" when you are guessing or talking about something you aren't completely sure about. If you were expressing a strong personal opinion rather than a guess, you would use a different verb: tycker.

Why does the verb tror end in just -r instead of -ar or -er?

Tror belongs to Group 3, which is a group of short verbs where the base form ends in a vowel, like att tro (to believe/think). To make these verbs present tense, you just add an -r to the end. Other common verbs in this group are bor (live) and mår (feel).

The English translation says "think so", but doesn't det mean "it" or "that"?

Exactly! In English we say "we don't think so", but the Swedish phrase is literally "we believe it not" (Vi tror inte det). The word det simply refers back to whatever idea or statement you are talking about.

Why does the negative word inte come after the verb?

Swedish uses the "V2 rule" for basic statements, meaning the verb must be in the second position of the sentence. Since Vi takes the first spot, the verb tror must be in the second spot. That pushes inte to the position directly after the verb.