How to sum() with multiplaction

sorry about the blank one... it was an accident

<node>
 <subnode1>test</subnode1>
 <subnode2>test</subnode2>
 <Node2>
   <test1>2</test1>
   <test2>25</test1>
</Node2>
 <Node2>
   <test1>3</test1>
   <test2>50</test1>
</Node2>

I want to get the sum of (in the test case)
2*25 and 3*50
So i want to get a result of 200
How do i do this? 
I have tried many different ways, with no luck.
Thanks
Joshua Smith

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