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.OutputStream;
  import java.io.IOException;
  import java.io.InputStream;
  import java.io.OutputStream;
  import java.io.PrintWriter;
  import java.io.BufferedWriter;
  import java.io.Writer;
  import java.io.OutputStreamWriter;
  import java.util.InputMismatchException;
  import java.io.IOException;
  import java.io.InputStream;
  
  /**
   * Built using CHelper plug-in
   * Actual solution is at the top
   *
   * @author iftekhar
   */
  public class Main {
    public static void main(String[] args) {
      InputStream inputStream = System.in;
      OutputStream outputStream = System.out;
      InputReader in = new InputReader(inputStream);
      OutputWriter out = new OutputWriter(outputStream);
      TaskA solver = new TaskA();
      solver.solve(1, in, out);
      out.close();
    }
  
    static class TaskA {
      public void solve(int testNumber, InputReader in, OutputWriter out) {
        int t = in.nextInt();
        while (t-- > 0) {
          int n = in.nextInt();
  
          int arr[] = in.nextIntArray(n);
          long max = arr[0];
          long sum = 0L;
          for (int i = 0; i < arr.length; i++) {
            sum += arr[i];
            if (max < arr[i]) {
              max = arr[i];
            }
          }
          double fb = (double) (sum - max) / (n - 1);
  
          out.println(String.format("%.9f", max + fb));
  
  
        }
      }
  
    }
  
    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]);
        }
      }
  
      public void println(Object... objects) {
        print(objects);
        writer.println();
      }
  
      public void close() {
        writer.close();
      }
  
    }
  
    static class InputReader {
      private InputStream stream;
      private byte[] buf = new byte[1024];
      private int curChar;
      private int numChars;
      private InputReader.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 nextInt() {
        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 boolean isSpaceChar(int c) {
        if (filter != null) {
          return filter.isSpaceChar(c);
        }
        return isWhitespace(c);
      }
  
      public static boolean isWhitespace(int c) {
        return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
      }
  
      public int[] nextIntArray(int n) {
        int[] array = new int[n];
        for (int i = 0; i < n; ++i) array[i] = nextInt();
        return array;
      }
  
      public interface SpaceCharFilter {
        public boolean isSpaceChar(int ch);
  
      }
  
    }
  }
  
  