1) You have syntax and logic errors, but overall you are reasonably close.
2) In the future, posted code is much easier to read if you wrap the code in code tags by first highlighting your code and then click the # icon in the editor's toolbar.
Code:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<script type="text/javascript">
function add(){
document.getElementById("answer").value+=(document.getElementById("num1").value) + "\n";
document.getElementById("num1").value = '';
document.getElementById("num1").focus();
}
function calculate(){
var total = 0, numCount = 0;
var sa = document.getElementById('answer').value.split("\n");
for (var i=0; i < sa.length; i++) {
if(!isNaN(parseFloat(sa[i]))){
total += parseFloat(sa[i]);
++numCount;
}
}
document.getElementById("sum").value = total;
document.getElementById("average").value = total / numCount;
}
</script>
</head>
<body>
<h1>Aggregates</h1>
<h3>Add as many numbers as you like<br>to the list,then click Calculate.</h3>
<form name="entryForm" id="entryForm">
<input type="text" id="num1" />
<input type="button" value="Add to list" onclick="add();"><br />
<textarea rows="15" cols="20" readonly="readonly" id="answer"></textarea><br />
<input type="button" value="Calculate" onclick="calculate();" />
<input type="reset" value="Reset" />
<p>Total (Sum);</p>
<input type="text" id="sum" value="0" /><br />
<p>Average :</p>
<input type="text" id="average" value="0" />
</form>
</body>
</html>