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: /**
   * check out my youtube channel sh0rkyboy
   * https://tinyurl.com/zdxe2y4z
   * I do screencasts, solutions, and other fun stuff in the future
   */
  
  import java.util.*;
  import java.io.*;
  import static java.lang.Math.min;
  import static java.lang.Math.abs;
  import static java.lang.Math.max;
  public class EdB {
  	static long[] mods = {1000000007, 998244353, 1000000009};
  	static long mod = mods[0];
  	public static MyScanner sc;
      public static PrintWriter out;
  	public static void main(String[] largewang) throws Exception{
  		// TODO Auto-generated method stub
   		sc = new MyScanner();
   		out = new PrintWriter(System.out);
   		int t = sc.nextInt();
   		while (t-->0) {
   			int n = sc.nextInt();
   			int[] arr = readArrayInt(n);
   			int max = -Integer.MIN_VALUE;
   			for(int j = 0;j<n;j++){
   				if (arr[j] > max) {
   					max = arr[j];
   				}
   			}
   			
   			out.println(max + (sum(arr)-max+0.0)/(n-1+0.0));
   		}
   		out.close();
   		
   	}
  	public static long sum(int[] array){
  		long sum = 0L;
  		for(int j : array){
  			sum += (long)j;
  			
  		}
  		return sum;
  	}
  	public static void sort(int[] array){
  		ArrayList<Integer> copy = new ArrayList<>();
  		for (int i : array)
  			copy.add(i);
  		Collections.sort(copy);
  		for(int i = 0;i<array.length;i++)
  			array[i] = copy.get(i);
  	}
  	static String[] readArrayString(int n){
  		String[] array = new String[n];
  		for(int j =0 ;j<n;j++)
  			array[j] = sc.next();
  		return array;
  	}
  	static int[] readArrayInt(int n){
      	int[] array = new int[n];
      	for(int j = 0;j<n;j++)
      		array[j] = sc.nextInt();
      	return array;
      }
  	static int[] readArrayInt1(int n){
  		int[] array = new int[n+1];
  		for(int j = 1;j<=n;j++){
  			array[j] = sc.nextInt();
  		}
  		return array;
  	}
  	static long[] readArrayLong(int n){
  		long[] array = new long[n];
  		for(int j =0 ;j<n;j++)
  			array[j] = sc.nextLong();
  		return array;
  	}
  	static double[] readArrayDouble(int n){
  		double[] array = new double[n];
  		for(int j =0 ;j<n;j++)
  			array[j] = sc.nextDouble();
  		return array;
  	}
  	static int minIndex(int[] array){
  		int minValue = Integer.MAX_VALUE;
  		int minIndex = -1;
  		for(int j = 0;j<array.length;j++){
  			if (array[j] < minValue){
  				minValue = array[j];
  				minIndex = j;
  			}
  		}
  		return minIndex;
  	}
  	static int minIndex(long[] array){
  		long minValue = Long.MAX_VALUE;
  		int minIndex = -1;
  		for(int j = 0;j<array.length;j++){
  			if (array[j] < minValue){
  				minValue = array[j];
  				minIndex = j;
  			}
  		}
  		return minIndex;
  	}
  	static int minIndex(double[] array){
  		double minValue = Double.MAX_VALUE;
  		int minIndex = -1;
  		for(int j = 0;j<array.length;j++){
  			if (array[j] < minValue){
  				minValue = array[j];
  				minIndex = j;
  			}
  		}
  		return minIndex;
  	}
  	static long power(long x, long y){
  		if (y == 0)
  			return 1;
  		if (y%2 == 1)
  			return (x*power(x, y-1))%mod;
  		return power((x*x)%mod, y/2)%mod;
  	}
  	static void verdict(boolean a){
          out.println(a ? "YES" : "NO");
      }
      public static class MyScanner {
          BufferedReader br;
          StringTokenizer st;
          public MyScanner() {
              br = new BufferedReader(new InputStreamReader(System.in));
          }
          String next() {
              while (st == null || !st.hasMoreElements()) {
                  try {
                      st = new StringTokenizer(br.readLine());
                  } 
                  catch (IOException e) {
                      e.printStackTrace();
                  }
              }
              return st.nextToken();
          }
          int nextInt() {
              return Integer.parseInt(next());
          }
          long nextLong() {
              return Long.parseLong(next());
          }
          double nextDouble() {
              return Double.parseDouble(next());
          }
          String nextLine() {
              String str = "";
              try{
                  str = br.readLine();
              } 
              catch (IOException e) {
                  e.printStackTrace();
              }
              return str;
          }
          
      }	
  }
  
  //StringJoiner sj = new StringJoiner(" "); 
  //sj.add(strings)
  //sj.toString() gives string of those stuff w spaces or whatever that sequence is