If we add math formula outside the Ng-App then that will not work whereas if we put that inside ngapp then the value will be calculated. See the code
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>Welcome to LearnKode - A code learning platform</title>
<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.4.2/angular.min.js"></script>
</head>
<body>
<div>
Out side from ng-app: {{2/2}}
</div>
<div ng-app>
In side ng-app: {{5/2}}
<div>
In side ng-app: {{10/2}}
</div>
</div>
<div>
Out side from ng-app: {{2/2}}
</div>
</body>
</html>
