SOURCE

<div id="outer-div">
    <div id="float-left">150 x 270 float:left</div>
    <div id="float-right">100 x 250 float:right</div>
    400 x 500
</div>

div{
    margin:5px;
}

#outer-div{
    height:400px;
    width:500px;
    background-color:red;
}

#float-left {
    height:150px;
    width:270px;
    float:left;
    background-color:blue;
}

#float-right{
    height:100px;
    width:250px;
    float:right;
    background-color:blue;
}
body{
    background-color:yellow
}