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.util.*;
   
  public class a {
      FastScanner scn;
      PrintWriter w;
      PrintStream fs;
  
      long MOD = 1000000007;
      int N=100000+10;
      long mul(long x, long y) {long res = x * y; return (res >= MOD ? res % MOD : res);}
      long power(long x, long y) {if (y < 0) return 1; long res = 1; x %= MOD; while (y!=0) {if ((y & 1)==1)res = mul(res, x); y >>= 1; x = mul(x, x);} return res;}
      boolean LOCAL;
      void debug(Object... o){if(LOCAL)System.err.println(Arrays.deepToString(o));}
      
      void solve(){
  
          int t=scn.nextInt();
              while(t-->0)
              {
                  int n=scn.nextInt();
                  double sum=0,max=-(double)1e13;
                  for(int i=1;i<=n;i++){
                      double v=scn.nextDouble();
                      sum+=v;
                      max=Math.max(max, v);
                  }
                  debug("max",max);
  
                  sum-=max;
                  
                  double ans=max+(sum/(n-1));
                  System.out.printf("%.9f",ans);
                  System.out.println();
              }
          
      }
   
      void run() {
          try {
              long ct = System.currentTimeMillis();
              scn = new FastScanner(new File("input.txt"));
              w = new PrintWriter(new File("output.txt"));
              fs=new PrintStream("error.txt");
              System.setErr(fs);
              LOCAL=true;
   
              solve();
   
              w.close();
              System.err.println(System.currentTimeMillis() - ct);
          } catch (FileNotFoundException e) {
              e.printStackTrace();
          }
      }
   
      void runIO() {
   
          scn = new FastScanner(System.in);
          w = new PrintWriter(System.out);
          LOCAL=false;
   
          solve();
   
          w.close();
      }
   
      class FastScanner {
          BufferedReader br;
          StringTokenizer st;
   
          public FastScanner(File f) {
              try {
                  br = new BufferedReader(new FileReader(f));
              } catch (FileNotFoundException e) {
                  e.printStackTrace();
              }
          }
   
          public FastScanner(InputStream f) {
              br = new BufferedReader(new InputStreamReader(f));
          }
   
          String next() {
              while (st == null || !st.hasMoreTokens()) {
                  String s = null;
                  try {
                      s = br.readLine();
                  } catch (IOException e) {
                      e.printStackTrace();
                  }
                  if (s == null)
                      return null;
                  st = new StringTokenizer(s);
              }
              return st.nextToken();
          }
   
          boolean hasMoreTokens() {
              while (st == null || !st.hasMoreTokens()) {
                  String s = null;
                  try {
                      s = br.readLine();
                  } catch (IOException e) {
                      e.printStackTrace();
                  }
                  if (s == null)
                      return false;
                  st = new StringTokenizer(s);
              }
              return true;
          }
   
          int nextInt() {
              return Integer.parseInt(next());
          }
          
          int[] nextIntArray(int n) {
              int a[] = new int[n];
              for (int i = 0; i < n; i++) {
                  a[i] = nextInt();
              }
              return a;
          }
  
          long[] nextLongArray(int n) {
              long a[] = new long[n];
              for (int i = 0; i < n; i++) {
                  a[i] = nextLong();
              }
              return a;
          }
  
          long nextLong() {
              return Long.parseLong(next());
          }
   
          double nextDouble() {
              return Double.parseDouble(next());
          }
      }
   
      public static void main(String[] args) {
          new a().runIO();
      }
  }
  