description: Ezzat has an array of n integers (maybe negative). He wants to split it into two non-empty subsequences a and b, such that every element from the array belongs to exactly one subsequence, and the value of f(a) + f(b) is the maximum possible value, where f(x) is the average of the subsequence x. 
  
  A sequence x is a subsequence of a sequence y if x can be obtained from y by deletion of several (possibly, zero or all) elements.
  
  The average of a subsequence is the sum of the numbers of this subsequence divided by the size of the subsequence.
  
  For example, the average of [1,5,6] is (1+5+6)/3 = 12/3 = 4, so f([1,5,6]) = 4.
  
  Input
  
  The first line contains a single integer t (1 ≤ t ≤ 10^3)— the number of test cases. Each test case consists of two lines.
  
  The first line contains a single integer n (2 ≤ n ≤ 10^5).
  
  The second line contains n integers a_1, a_2, …, a_n (-10^9 ≤ a_i ≤ 10^9).
  
  It is guaranteed that the sum of n over all test cases does not exceed 3⋅10^5.
  
  Output
  
  For each test case, print a single value — the maximum value that Ezzat can achieve.
  
  Your answer is considered correct if its absolute or relative error does not exceed 10^{-6}.
  
  Formally, let your answer be a, and the jury's answer be b. Your answer is accepted if and only if \frac{|a - b|}{max{(1, |b|)}} ≤ 10^{-6}.
  
  Example
  
  Input
  
  
  4
  3
  3 1 2
  3
  -7 -6 -6
  3
  2 2 2
  4
  17 3 5 -3
  
  
  Output
  
  
  4.500000000
  -12.500000000
  4.000000000
  18.666666667
  
  Note
  
  In the first test case, the array is [3, 1, 2]. These are all the possible ways to split this array: 
  
    * a = [3], b = [1,2], so the value of f(a) + f(b) = 3 + 1.5 = 4.5. 
    * a = [3,1], b = [2], so the value of f(a) + f(b) = 2 + 2 = 4. 
    * a = [3,2], b = [1], so the value of f(a) + f(b) = 2.5 + 1 = 3.5. 
  
  Therefore, the maximum possible value 4.5.
  
  In the second test case, the array is [-7, -6, -6]. These are all the possible ways to split this array: 
  
    * a = [-7], b = [-6,-6], so the value of f(a) + f(b) = (-7) + (-6) = -13. 
    * a = [-7,-6], b = [-6], so the value of f(a) + f(b) = (-6.5) + (-6) = -12.5. 
  
  Therefore, the maximum possible value -12.5.
solution: import java.io.BufferedReader;
  import java.io.IOException;
  import java.io.InputStreamReader;
  import java.math.BigDecimal;
  import java.util.ArrayList;
  import java.util.Arrays;
  import java.util.Random;
  import java.util.StringTokenizer;
  public class B{
  // author: Tarun Verma
  static FastScanner sc = new FastScanner();
  static int inf = Integer.MAX_VALUE;
  static long mod = 1000000007;
  
  public static void solve() {
  	int n = sc.nextInt();
  	int arr[] = sc.readArray(n);
  	ruffleSort(arr);
  	long a = arr[n-1];
  	long b= 0;
  	for(int i =0;i<n-1;i++) {
  		 b += arr[i];
  	}
  //	System.out.println(b);
  //	System.out.println(n-1);
  	double ans = b / (double)(n-1);
  //	System.out.println(ans);
  	ans += a;
  	System.out.println(ans);
  }
  
  public static void main(String[] args) {
  	int t = 1;
  	t = sc.nextInt();
  	outer: for (int tt = 0; tt < t; tt++) {
  		solve();
  	}
  }
  /* Common Mistakes By Me
   * make sure to read the bottom part of question
   * special cases (n=1?)
   * In Game Theory Check your solution and consider all the solutions
   * Always initialise value to the declare array in local scope
   * don't use debugs in interactive problems
   * Always Reset vis,adj array upto n+1 otherwise can cause TLE
  */
  ////////////////////////////////////////////////////////////////////////////////////
  ////////////////////DO NOT BELOW BEFORE THIS LINE //////////////////////////////////
  ////////////////////////////////////////////////////////////////////////////////////
  
  static boolean isPalindrom(char[] arr, int i, int j) {
  	boolean ok = true;
  	while (i <= j) {
  		if (arr[i] != arr[j]) {
  			ok = false;
  			break;
  		}
  		i++;
  		j--;
  	}
  	return ok;
  }
  
  static int max(int a, int b) {
  	return Math.max(a, b);
  }
  
  static int min(int a, int b) {
  	return Math.min(a, b);
  }
  
  static long max(long a, long b) {
  	return Math.max(a, b);
  }
  
  static long min(long a, long b) {
  	return Math.min(a, b);
  }
  
  static int abs(int a) {
  	return Math.abs(a);
  }
  
  static long abs(long a) {
  	return Math.abs(a);
  }
  
  static void swap(long arr[], int i, int j) {
  	long temp = arr[i];
  	arr[i] = arr[j];
  	arr[j] = temp;
  }
  
  static void swap(int arr[], int i, int j) {
  	int temp = arr[i];
  	arr[i] = arr[j];
  	arr[j] = temp;
  }
  
  static int maxArr(int arr[]) {
  	int maxi = Integer.MIN_VALUE;
  	for (int x : arr)
  		maxi = max(maxi, x);
  	return maxi;
  }
  
  static int minArr(int arr[]) {
  	int mini = Integer.MAX_VALUE;
  	for (int x : arr)
  		mini = min(mini, x);
  	return mini;
  }
  
  static long maxArr(long arr[]) {
  	long maxi = Long.MIN_VALUE;
  	for (long x : arr)
  		maxi = max(maxi, x);
  	return maxi;
  }
  
  static long minArr(long arr[]) {
  	long mini = Long.MAX_VALUE;
  	for (long x : arr)
  		mini = min(mini, x);
  	return mini;
  }
  
  static int gcd(int a, int b) {
  	if (b == 0)
  		return a;
  	return gcd(b, a % b);
  }
  
  static long gcd(long a, long b) {
  	if (b == 0)
  		return a;
  	return gcd(b, a % b);
  }
  
  static void ruffleSort(int[] a) {
  	int n = a.length;
  	Random r = new Random();
  	for (int i = 0; i < a.length; i++) {
  		int oi = r.nextInt(n);
  		int temp = a[i];
  		a[i] = a[oi];
  		a[oi] = temp;
  	}
  	Arrays.sort(a);
  }
  
  public static int binarySearch(int a[], int target) {
  	int left = 0;
  	int right = a.length - 1;
  	int mid = (left + right) / 2;
  	int i = 0;
  	while (left <= right) {
  		if (a[mid] <= target) {
  			i = mid + 1;
  			left = mid + 1;
  		} else {
  			right = mid - 1;
  		}
  		mid = (left + right) / 2;
  	}
  	return i;
  }
  
  static class FastScanner {
  	BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
  	StringTokenizer st = new StringTokenizer("");
  
  	String next() {
  		while (!st.hasMoreTokens())
  			try {
  				st = new StringTokenizer(br.readLine());
  			} catch (IOException e) {
  				e.printStackTrace();
  			}
  		return st.nextToken();
  	}
  
  	int nextInt() {
  		return Integer.parseInt(next());
  	}
  
  	int[] readArray(int n) {
  		int[] a = new int[n];
  		for (int i = 0; i < n; i++)
  			a[i] = nextInt();
  		return a;
  	}
  
  	int[][] read2dArray(int n, int m) {
  		int arr[][] = new int[n][m];
  		for (int i = 0; i < n; i++) {
  			for (int j = 0; j < m; j++) {
  				arr[i][j] = nextInt();
  			}
  		}
  		return arr;
  	}
  
  	ArrayList<Integer> readArrayList(int n) {
  		ArrayList<Integer> arr = new ArrayList<Integer>();
  		for (int i = 0; i < n; i++) {
  			int a = nextInt();
  			arr.add(a);
  		}
  		return arr;
  	}
  
  	long nextLong() {
  		return Long.parseLong(next());
  	}
  }
  
  static class pair {
  	int fr, sc;
  
  	pair(int fr, int sc) {
  		this.fr = fr;
  		this.sc = sc;
  	}
  }
  
  ////////////////////////////////////////////////////////////////////////////////////	
  
  }