<!DOCTYPE html>
<html>
<head>
<script src="http://code.jquery.com/jquery-1.8.2.min.js"></script>
<script>
$(document).ready(function(){
$("button").click(function(){
var s1= $("#s1").val();
var s2=$("#s2").val();
var toplam=parseInt(s1)+parseInt(s2);
$("#sonuc").val(toplam);
});
});
</script>
</head>
<body>
<select id="s1">
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
<option value="4">4</option>
</select>
<select id="s2">
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
<option value="4">4</option>
</select>
<input type="text" name="sonuc" id="sonuc">
<button>Click me</button>
</body>
</html>