I got the answer to this back in the 5th grade. I assume this should take you guys no more than five minutes tops.
You start with this shape.
You can add only four straight lines, and you must end up with ten boxes of equal size. No loose ends of lines can be hanging out, either.
Good luck. In ten minutes, I want to be able to come back to this thread and see that someone has solved it…
here ya go.
Well, I can’t provide you with an image per se, so I’ll try to give you the ASCII version:
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Took me longer to type that than it did to solve it. 
DOH! Crap, spaces at beginning of lines don’t work.
10 seconds, here you go…
extend the lines through the middle of the two boxes to form a third to the right of and above the other two with two lines and seal the edges with the other two lines.
My drawing sucked, but it worked. Thanks for the tickle.
Yeah, you got it.