<style>
body{
    margin:0;
}
#m{
position:absolute;
left:0;top:0;
width:190px;
 background: #f22121;
}

#n{
 background: green; 
margin:0px 190px 0px 190px;
}

#b{
position:absolute;
right:0;top:0;
width:190px;
 background: #f22121;
}
</style>

<body>
  <div id="m">左DIV</div>
  <div id="n">  中间DIV</div>
  <div id="b">右DIV</div>
</body>