"How many minutes are there in an hour?"
Translation:एक घंटे में कितने मिनट होते हैं?
It's not plural. It just appears so because it is in the oblique case, ie, followed by a postposition (में).
It's because we are talking about a universal truth (the number of minutes in an hour) here. होते is used for such sentences and when you are making generalizations.
I'm very confused about when duolingo wants a literal translation, for which te he English equivalent would be "in one hour, how many minutes are there?", vs a more natural expression of the idea. When doing comparisons they preferred literal ones (making distinction between "this book is the best" and "this is the best book"!