Good Riddles

Question: If you have an 11 minute and 13 minute hourglass, how can you accurately time 15 minutes?

Question: A teacher decides to give a pop quiz one day but all of her students refuse to take the quiz thinking that the teacher will call off the quiz. She can give only one of these students a detention for skipping the quiz. All of the students know each other's names and if a student knows he/she is getting a detention they take the quiz.

How can she threaten her students with the single detention so they all take the quiz?

Question: No matter how much rain comes down on it it won't get any wetter.

What is it?

Question: There are two planes. One is going from New York to London at a speed of 600 MPH. The other is traveling from London to New York at a speed of 500 MPH.

When the planes meet which one will be closer to London?

Question: Many have heard me, but nobody has seen me, and I will not speak back until spoken to.What am I?