Subject: Engineer & Mathematician

The difference between an Engineer and a Mathematician :
 
  The Engineer walks in her office and finds her trash can on fire.  She
gets the fire extinguisher and puts out the fire.
 
  The Mathematician walks in his office and finds his trash can on fire.
He gets the fire extinguisher and puts out the fire.

  The following day :

  The Engineer walks in her office and finds the trash can on fire on
top of her desk.  She gets the fire extinguisher and put out the fire.
 
  The Mathematician walks in his office and finds the trash can on fire
on top of his desk.  He takes the trash can and puts it on the floor.
He has reduced the problem to a previously solved state.  Too solve it
again would be redundant.