Why `float:left` doesn't work with a fixed width?

Question

I have two divs on a webpage and I would like both of them to have a fixed width and would like the first div to be floated to the left of the second div.

This sound

Answer 1

 div.left {
     float: left;
     width: 200px;
    height:200px;
    background:red;
 }

 div.right {
    float:right;
     width: 200px;
     height:200px;
    background:blue;
}

see http://jsfiddle.net/3kUpF/

Alternatively, if you want them side by side then you can float:left on both see http://jsfiddle.net/3kUpF/1/