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.*;
      import java.util.InputMismatchException;
   
  public class Cf {
       int mod = (int)1e9+7;
      public static void main(String[] args) throws Exception {
          Cf cf = new Cf();
          cf.solve();
      }
      public void solve() {
          InputReader in = new InputReader(System.in);
          OutputWriter out = new OutputWriter(System.out);
          //Union un = new Union();
          int t = in.readInt();
          while(t--!=0) {
              int n = in.readInt();
              long arr[] = new long[n];
              long max = Long.MIN_VALUE;
              for(int i=0;i<n;i++) {
                  arr[i] = in.readLong();
                  if(arr[i]>max) {
                      max = arr[i];
                  }
              }
              boolean flag = false;
              double ans = 0.000000000;
              for(int i=0;i<n;i++) {
                  if(arr[i]==max & !flag) {
                      flag = true;
                      continue;
                  }
                  ans+=(double)arr[i];
              }
              ans = ans/(n-1);
              ans+=(double)max;
              out.printLine(String.format("%.9f", ans));
          }
         
          
                      
      }
      //logn time
      public long findPower(long x,long n) {
          long ans = 1;
          long nn = n;
          while(nn>0) {
              if(nn%2==1) {
                  ans = (ans*x) % mod;
                  nn-=1;
              }else {
                  x = (x*x)%mod;
                  nn/=2;
              }
          }
          return ans%mod;
      }
       
          //FAST IO
          private static class InputReader {
              private InputStream stream;
              private byte[] buf = new byte[1024];
              private int curChar;
              private int numChars;
              private SpaceCharFilter filter;
       
              public InputReader(InputStream stream) {
                  this.stream = stream;
              }
       
              public int read() {
                  if (numChars == -1) {
                      throw new InputMismatchException();
                  }
                  if (curChar >= numChars) {
                      curChar = 0;
                      try {
                          numChars = stream.read(buf);
                      } catch (IOException e) {
                          throw new InputMismatchException();
                      }
                      if (numChars <= 0) {
                          return -1;
                      }
                  }
                  return buf[curChar++];
              }
       
              public int readInt() {
                  int c = read();
                  while (isSpaceChar(c)) {
                      c = read();
                  }
                  int sgn = 1;
                  if (c == '-') {
                      sgn = -1;
                      c = read();
                  }
                  int res = 0;
                  do {
                      if (c < '0' || c > '9') {
                          throw new InputMismatchException();
                      }
                      res *= 10;
                      res += c - '0';
                      c = read();
                  } while (!isSpaceChar(c));
                  return res * sgn;
              }
       
              public String readString() {
                  int c = read();
                  while (isSpaceChar(c)) {
                      c = read();
                  }
                  StringBuilder res = new StringBuilder();
                  do {
                      res.appendCodePoint(c);
                      c = read();
                  } while (!isSpaceChar(c));
                  return res.toString();
              }
       
              public double readDouble() {
                  int c = read();
                  while (isSpaceChar(c)) {
                      c = read();
                  }
                  int sgn = 1;
                  if (c == '-') {
                      sgn = -1;
                      c = read();
                  }
                  double res = 0;
                  while (!isSpaceChar(c) && c != '.') {
                      if (c == 'e' || c == 'E') {
                          return res * Math.pow(10, readInt());
                      }
                      if (c < '0' || c > '9') {
                          throw new InputMismatchException();
                      }
                      res *= 10;
                      res += c - '0';
                      c = read();
                  }
                  if (c == '.') {
                      c = read();
                      double m = 1;
                      while (!isSpaceChar(c)) {
                          if (c == 'e' || c == 'E') {
                              return res * Math.pow(10, readInt());
                          }
                          if (c < '0' || c > '9') {
                              throw new InputMismatchException();
                          }
                          m /= 10;
                          res += (c - '0') * m;
                          c = read();
                      }
                  }
                  return res * sgn;
              }
       
              public long readLong() {
                  int c = read();
                  while (isSpaceChar(c)) {
                      c = read();
                  }
                  int sgn = 1;
                  if (c == '-') {
                      sgn = -1;
                      c = read();
                  }
                  long res = 0;
                  do {
                      if (c < '0' || c > '9') {
                          throw new InputMismatchException();
                      }
                      res *= 10;
                      res += c - '0';
                      c = read();
                  } while (!isSpaceChar(c));
                  return res * sgn;
              }
       
              public boolean isSpaceChar(int c) {
                  if (filter != null) {
                      return filter.isSpaceChar(c);
                  }
                  return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
              }
       
              public String next() {
                  return readString();
              }
       
              public interface SpaceCharFilter {
                  public boolean isSpaceChar(int ch);
              }
          }
       
          private static class OutputWriter {
              private final PrintWriter writer;
       
              public OutputWriter(OutputStream outputStream) {
                  writer = new PrintWriter(new BufferedWriter(new OutputStreamWriter(outputStream)));
              }
       
              public OutputWriter(Writer writer) {
                  this.writer = new PrintWriter(writer);
              }
       
              public void print(Object... objects) {
                  for (int i = 0; i < objects.length; i++) {
                      if (i != 0) {
                          writer.print(' ');
                      }
                      writer.print(objects[i]);
                  }
                  writer.flush();
              }
       
              public void printLine(Object... objects) {
                  print(objects);
                  writer.println();
                  writer.flush();
              }
       
              public void close() {
                  writer.close();
              }
       
              public void flush() {
                  writer.flush();
              }
          }
      }