Not too long ago, if I had to ask my teacher at school if could go to the toilet, the right way to do it was to raise your hand and say: "May I go to the toilet?" Any other way of formulating the question would have resulted in a forehand slap on the back of my head. Yes it was legal to smack students at school! Well, it has been a really long time since I went to school, things have changed.
Now you don't get smacked on the back of your head and now you don't need to use certain grammar rules which were sacred no too long ago.
I remember that ending a question with a preposition was so wrong, it would just disgust my teacher so much she would actually make me write "I won't use prepositions at the end of a question" a hundred times. (Like that ever helped me learn the lesson!) In fact, today using a preposition at the end of a question is the most common and stylish way to formulate questions. There's no academic rule against it.
Read this wonderful article by Lisa Muzaffar here, and get to know all of the secrets of English you were never told about!