"Did you find?"
I know the French say this, but the English translation is grammatically incorrect. You can't say "did you find" without an object. It has to be "did you find IT". Unfortunately, of course, this would naturally translate to "tu l'as trouvé?", which is not what they're going for here... tricky!
Actually it is rare that the preterit translates in the imparfait and vice-versa.
On top of it, "tu trouvais ?" does not have much sense, except in a figurative sense of "trouver" to mean "feel, think, believe", and rather in the present tense:
- il fait froid ici (it's cold here)
- tu trouves? (is it? or do you feel so?)
Sorry if my comment looks irrelevant but if you read it carefully, you should have understood that the translation proposed by Duolingo is wrong because the French imparfait is rarely a correct translation for the English preterit.
That comment was supporting Gregkaleka's suggestion to use the passé composé.
Now, it is not compulsory that an object is added to that question. In informal conversations, you can say "tu as trouvé ?" without "l' " (it).