<html>
<head>
  <title>Div example</title>
</head>
<body>

<style type="text/css"> 
.left {
  float: left;
  width: 120px;
  height: 40px;
  border: 1px solid;
}

.left_dummy {
  float: left;
  width: 100%;
  height: 50px;
  border: 1px dotted;
}

.right {
  float: right;
  width: 120px;
  height: 40px;
  border: 1px solid;
}
</style>

<div class="left">
  1
</div>

<div class="right">
  2
</div>

<div class="left_dummy">&nbsp;</div>

<div class="left">
  3
</div>

<div class="right">
  4
</div>

</body>
</html>