How to make a div align to the right side of the parent while maintaining its vertical position?

Question

Please refer to this handy diagram I drew:

div1's height is unknown. div3's width is fluid; it should never overlap div2. Both div1 and div2 have the same width and are horizontally centered via margin: auto. How can I position div3 so that it aligns to the right side of body (no matter how wide body is) while sharing vertical position with div2? (Using CSS)

Answer 1

.div1{
    margin:0 auto;
    width:100px;
    height:50px;
    border:5px solid #995555;
}
.div2{
    width:100px;
    margin:0 auto;
    border:5px solid #aaaa55;
    height:200px;
}
.div3{
    float:right;
    width:50px;
    height:100px;
    border:5px solid cyan;
}

<div class="div1">div1</div>
<div class="div3">div3</div>
<div class="div2">div2</div>

Demo also at http://jsfiddle.net/XjC9z/1/