This is the modified codes to calculate average score.

averageScore_OK.js

function averageScore(arr) {
    var total = 0;
    for (var i = 0; i < arr.length; i++) {
        total += arr[i];
    }
    return total / arr.length;
}

// Another solution:
var averageScore = function (arr) {
    var total = 0;
    arr.forEach(function (elem) {
        total += elem
    });
    return total / arr.length;
}