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.*;
  import java.math.*;
  import java.sql.Array;
  import java.util.*;
  
  public class Main {
  
      static final int MAX_N = 1000010;
      static final int INF = 0x3f3f3f3f;
  
      public static void main(String[] args) throws IOException {
          initReader(System.in);
  
  
          int T = nextInt();
          for (int i = 1; i <= T; i++)
          solve();
  
  
          pw.flush();
      }
  
  
      /*******************************************************************************************************************************/
  
  
      public static void solve() throws IOException {
          int n = nextInt();
  
          int[] a = new int[n];
  
          long sum1 = 0;
          long sum2 = 0;
          for (int i = 0; i < n; i++) {
              a[i] = nextInt();
              sum1 += a[i];
          }
  
          shuffle(a);
          Arrays.sort(a);
  
          double ans = Long.MIN_VALUE;
          for (int i = 0; i < n - 1; i++) {
              sum1 -= a[i];
              sum2 += a[i];
              ans = Math.max(ans, (double) sum1 / (n - i - 1) + (double) sum2 / (i + 1));
          }
  
          pw.println(String.format("%.10f", ans));
      }
  
      public static void shuffle(int[] a) {
          for (int i = 0; i < a.length; i++) {
              int rand = (int) (Math.random() * a.length);
              int temp = a[rand];
              a[rand] = a[i];
              a[i] = temp;
          }
      }
  
  
      /*******************************************************************************************************************************/
  
  
      /*******************************************************************************************************************************/
  
      static BufferedReader reader;
      static StringTokenizer tokenizer;
      static PrintWriter pw;
  
      public static void initReader(InputStream input) throws IOException {
          reader = new BufferedReader(new InputStreamReader(input));
          tokenizer = new StringTokenizer("");
          pw = new PrintWriter(new BufferedWriter(new OutputStreamWriter(System.out)));
  
  //        reader = new BufferedReader(new FileReader("test.in"));
  //        tokenizer = new StringTokenizer("");
  //        pw = new PrintWriter(new BufferedWriter(new FileWriter("test1.out")));
      }
  
      public static boolean hasNext() {
          try {
              while (!tokenizer.hasMoreTokens()) {
                  tokenizer = new StringTokenizer(reader.readLine());
              }
          } catch (Exception e) {
              return false;
          }
          return true;
      }
  
      public static String next() throws IOException {
          while (!tokenizer.hasMoreTokens()) {
              tokenizer = new StringTokenizer(reader.readLine());
          }
          return tokenizer.nextToken();
      }
  
      public static String nextLine() {
          try {
              return reader.readLine();
          } catch (Exception e) {
              return null;
          }
      }
  
      public static int nextInt() throws IOException {
          return Integer.parseInt(next());
      }
  
      public static long nextLong() throws IOException {
          return Long.parseLong(next());
      }
  
      public static double nextDouble() throws IOException {
          return Double.parseDouble(next());
      }
  
      public static char nextChar() throws IOException {
          return next().charAt(0);
      }
  
      public static short nextShort() throws IOException {
          return Short.parseShort(next());
      }
  
  }
  
  
  