title: Find from a hashtable using the value
body: <p>I have a following hash table:</p>
  
  <pre><code>private Hashtable Sid2Pid = new Hashtable();
  
  Sid2Pid.Add(1,10);
  Sid2Pid.Add(2,20);
  Sid2Pid.Add(3,20);
  Sid2Pid.Add(4,30);
  </code></pre>
  
  <p>Now how to get the list of keys from the above hashtable that has a value of 20 using LinQ</p>