求高手解答，急
<title>系好安全带,准备启航</title>
<script type="text/javascript">
var myday = new Date();
var weekday = ["星期日", "星期一", "星期二", "星期三", "星期四", "星期五", "星期六"];
document.write(myday.getFullYear() + "年" + myday.getMonth() + "月" + myday.getDate() + "日"+weekday[myday.getDay()]);
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 all=scoreStr.split(";");
var sum=0;
for (var i = 0; i < all.length; i ++) {
sum += parseInt(all[i].substr(all[i].indexOf(":")+1));
//document.write("<br>" + sum);//test
}
document.write(sum+"</br>");
document.write(all.length+"</br>")
document.write(Math.round(sum/all.length));
</script>
</head>
<body>
请教高手，为什么我最后哪里不加parseInt就没有结果了，明明是两个数字类型啊？help。
