#include <iostream>
using namespace std;

void q_sort(int nums[], int left, int right);
void QuickSort(int nums[], int size)
{
    q_sort(nums, 0, size - 1);
}

void q_sort(int numbers[], int left, int right)
{
    if (left == right) return;
    int pivot, l_hold, r_hold;
    l_hold = left;
    r_hold = right;
    pivot = numbers[left];

    while (left < right)
    {
        while ((numbers[right] >= pivot) && (left < right))
            right--;
        if (left != right)
        {
            numbers[left] = numbers[right];
            left++;
        }

        while ((numbers[left] <= pivot) && (left < right))
            left++;

        if (left != right)
        {
            numbers[right] = numbers[left];
            right--;
        }
    }

    numbers[left] = pivot;
    pivot = left;
    left = l_hold;
    right = r_hold;

    if (left < pivot)
        q_sort(numbers, left, pivot - 1);
    if (right > pivot)
        q_sort(numbers, pivot + 1, right);
}

float GetAverage(float s1, float s2)
{
    return (s1 + s2) / 2;
}
int main()
{
    int t; // t <= 50
    int n; // 3 <= n <= 40
    cin >> t;
    while (t--)
    {
        float maxScore = 0;
        cin >> n;
        int* score = new int[n];

        for (int i = 0; i < n; i++)
        {
            cin >> score[i]; // 0점 이상 100점 이하
        }

        QuickSort(score, n);

        int tempIndex = n - 1;
        float tempScore = 0;
        for (int i = 0; i < n; i++)
        {
            tempScore = GetAverage(score[i], score[tempIndex]);
            if (maxScore < tempScore)
            {
                maxScore = tempScore;
            }
            tempIndex--;
        }

        cout << fixed;
        cout.precision(1);
        cout << maxScore;
    }
}