Do not have multiple References of same JS Files as it will slow down your application.
Just Refer to these Files in Your Master page once:
<link rel="stylesheet" href="http://ajax.googleapis.com/ajax/libs/jqueryui/1.8.17/themes/pepper-grinder/jquery-ui.css" />
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.min.js"></script>
<script src="https://ajax.googleapis.com/ajax/libs/jqueryui/1.8.17/jquery-ui.min.js"></script>