title: How to convert NSNumber objects for computational purposes?
body: <p>I an developing some code in which I use a scanner to get to NSNumbers from a string, say x and y.</p>
  
  <p>Now I want to compute something simple from x and y, say, z = 10.0/(x + y/60.0)/60.0). I can't do this directly, since the compiler doesn't like ordinary arithmetic symbology applied to number objects.</p>
  
  <p>So, I tried defining xD and yD, of type double, and then tried a type conversion</p>
  
  <p>xD = (double) x;
     yD = (double) y;</p>
  
  <p>but that also gives a compile error.  Just how does one get NSNumber objects converted to be used in ordinary arithmetic expressions?  I did considerable browsing of the literature, and didn't find the answer.</p>
  
  <p>Thanks in advance for any help.</p>
  
  <p>John Doner</p>