提供一个标准答案，为了思路看起来更清晰，输出了格式有点不一样
<!DOCTYPE HTML>
<html >
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>系好安全带,准备启航</title>
<script type="text/javascript">
//通过javascript的日期对象来得到当前的日期，并输出。
var mydate = new Date();
var year = mydate.getFullYear();
var month = mydate.getMonth()+1;
var day = mydate.getDate();
var weekdays = ["星期日","星期一","星期二","星期三","星期四","星期五","星期六"];
var weekday = weekdays[mydate.getDay()];
document.write(year+"年"+month+"月"+day+"日"+" "+weekday+"<br>");
//成绩是一长窜的字符串不好处理，找规律后分割放到数组里更好操作哦
var scoreStr = "小明:87;小花:81;小红:97;小天:76;小张:74;小小:94;小西:90;小伍:76;小迪:64;小曼:76";
var scoreArr = scoreStr.split(";");
//从数组中将成绩撮出来，然后求和取整，并输出
var num = new Array();
var sum = 0;
for(var i=0; i<scoreArr.length; i++){
num[i] = scoreArr[i].substring(3);
sum += parseInt(num[i]);
}
document.write("班级总分为："+sum+"<br>");
var average = Math.round(sum/scoreArr.length);
document.write("班级平均分为："+average);
</script>
</head>
<body>
</body>
</html>
