title: Magento Event Before Adding a Product to Cart
body: <p>I want to calculate price based on the customer selected options.
  For example,there are two configurable attributes <code>length,width</code></p>
  
  <p>Before adding product to cart,I want to modify price based on selected length &amp; width</p>
  
  <pre><code>$finalPrice=$rrp+($length*$width)
  </code></pre>
  
  <p>Is there any event available to achieve this?</p>