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// optAvg([2,3,5], 20)
// => [9.67741935483871, 6.451612903225807, 3.870967741935484]

function optAvg(list, total) {
    var ratio = 0;
    var rtn = [];
    var i, avg, bs;

    for (i = list.length; i--; ) {
        ratio += 1 / list[i];
    }
    
    // 平均数
    avg = total / ratio;

    for (i = list.length; i--; ) {
        // 倍数
        bs = avg / list[i];
        rtn[i] = bs;
    }

    return rtn;
}