title: Big-O Notation of multiple statements
body: <p>Suppose there are multiple functions with certain big o notations, anything O(N), O(N^2), etc.
  If you have a code fragment such as.</p>
  
  <pre><code> f1(x);
   f2(x);
   f3(x);
  </code></pre>
  
  <p>Are all the big O notations added together or multiplied? Any explanation as to why either would be correct - addition or multiplication? </p>