No argument with no return value in js.html

<html>

<head>
	<script type="text/javascript">
		function calculate() {

			var a = 20;
			var b = 30;
			var sum = 0;
			var avg;
			sum = a + b;
			document.write("sum of value are:" + sum + "<br>");
			avg = sum / 2;
			document.write("average of value is:" + avg);
		}
	</script>
</head>

<body>
	<script type="text/javascript">
		calculate();
	</script>
</body>

</html>