Wouldn't ¿Crees que has aprobado el examen? be "Do you think you have passed the exam?" I don't know the grammatical tense that applies, but on the face of it, it seems the "have" should be represented in the English.
Also, does Spanish have an equivalent of "do?" I think i read that it does not. In English it is often ommitted, so it's probably ok to not always include it in translations.