Summing grouped elements

Hi  people . David Carlisle , I'm Sorry.  I think that I became my
problem in some very complex
 hard to understand.

I translate it this way:  If i have this XML

<cars> 
   <car>
		<model>V667320</model>
		<name>Sportage</name>
                <categ>sport</categ>

   </car>
   <car>
		<model>M382932</model>
		<name>Silverado</name>
               <categ>pick-up</categ>
 </car>
 <car>
		<model>L930389</model>
		<name>Jaguar</name>
                <categ>Sport</categ>
  </car>
  <car>
		<model>J980384</model>
		<name>Ranger</name>
                <categ>Pick-up</categ>
  </car>
</cars>

I Think  through this example you'll understand what I want to do.  

The question: I have Two categories: sport and Pick-up. Ok? 

How can I  using XSL to obtain the Total value by category, in this
case  = 2 ?     Thanks .


  Marcos Hercules dos Santos