title: NSDate (Time Elapsed) to Hours
body: <p>I am trying to calculate the average speed of the user using Core Location, so I have a total distance traveled in miles (<code>double totalDistance</code>) and the time elapsed (<code>NSDate *timeElapsed</code>).</p>
  
  <p>How can I convert <code>timeElapsed</code> to a double displaying hours? I.e. 0.1 hours, 0.0001 hours, etc so that I can calculate my average speed correctly?</p>