Got a really simple question: if I have a 400px wide div, and in in two floating 200px wide divs, why won't they align properly?

Code:
<div style="background-color: #000000; width:400px; height:300px; padding:0; margin:0">
* <div  style="background-color:#f000aa;  padding:0;  margin:0;  height:100px;  width:200px;  float:right;"></div>
* <div  style="background-color:#f0f0ee;  padding:0;  margin:0;  height:100px;  width:200px;  float:left;"></div>
</div>
you can see they have margin and padding set to 0 so I don't understand what's going on (screenshot attached)
blocks.png