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<head>
<meta http-equiv="Content-Type" content="text/html;charset=UTF-8">
<title>Document</title>
</head>
<script>
function fun(arr){
var sum=0;
var len=arr.length; //用len表示数组的长度
for(var i=0;i<len;i++)
{
sum=sum+arr[i];
}
var pingjunzhi=sum/len;
return pingjunzhi;
}
var a=[10,20,30,40]; //声明数组用的是中括号，不是大括号
alert(fun(a));
</script>
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</body>
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