"Why is your secretary sleeping?"
Translation:למה המזכיר שלך ישן?
Well, מַדּוּעַ is decisively more formal than לָ֫מָּה, having being abandoned in rabbinic Hebrew. By the way, it should have had originally another shade of meaning: being a contraction of מַה־יָּדוּעַ what is known, it should ask for the causes and reasons (German warum), whereas לָ֫מָּה, literally for what (German wozu), should ask for purpose. So an answer to מַדּוּעַ should be because he has worked too much, but to לָ֫מָּה in order to resume his work refreshed But this difference of sense has been blurred to a difference of formality.