con add()
Código HTML:
<!DOCTYPE html>
<html>
<head>
<script src="http://code.jquery.com/jquery-latest.js"></script>
</head>
<body>
<div>div 1</div>
<div>div 2</div>
<p>p 1</p>
<p>p 2</p>
<script>
div = $("div");
p = $("p");
divp = div.add(p);
alert ("div "+div.length);
alert ("p "+div.length);
alert ("div y p "+divp.length);
</script>
</body>
</html>