Przedmiot as a thing i.e. a book, a pen, a wallet etc.
Another valid translation is 'I have ten subjects' as school activities.
Subjects sounds like the underlings of a king.
If you're going to use przedmioty in the sense of school subjects, then a correct English translation would include "I'm taking ten courses". Nobody says "I have ten subjects" when speaking about their class load.
But I removed "subjects" from the best answers, let's make it just accepted.
I would have said that I was doing eight subjects, when I was at school (in the UK). University students would talk about courses, or maybe units.