What's 1+1? There are some answers to this question in our 
Dr. Math archives:

   1 + 1
   Does 1 + 1 make 2 or 11?
   
   What is 1 plus 1?
   What is 1 plus 1?
   
   One Plus One
   Are you sure that 1 plus 1 equals 2?
   
   Proof that 1 + 1 = 1?
   Can you shed any light on this subject?
   
   Proof that 1 + 1 = 2
   Can you prove that 1 + 1 = 2?