title: Sum DataTable columns of type string
body: <p>How do I calculate Sum of two rows in <code>DataTable</code> which is of type string ?<br>
  in my case I cannot change column type.<br>
  I tried these :  </p>
  
  <p>1)</p>
  
  <pre><code>object objSum;    
  objSum = dt.Compute("Sum(WeightRate)", "");     
  </code></pre>
  
  <p>2)    </p>
  
  <pre><code>decimal total = (decimal)dt.Compute("SUM( [WeightRate] )", "");`   
  </code></pre>
  
  <p>But no luck...</p>
  
  <p>My table :  </p>
  
  <blockquote>
    <p>Weightrate         No.Ofvehicles<br>
      350.50              50<br>
      205.00               40</p>
  </blockquote>
  
  <p>I need result as   </p>
  
  <blockquote>
    <p>Weightrate         No.Ofvehicle<br>
      555.50              90</p>
  </blockquote>