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: """..::::::::::::..:::::..:::::..:::::..::::::::..::::::::..:::::..:::
  '########::::::::'###:::::::'########:::::'########::::'##::::'##:::::
   ##.... ##::::::'## ##:::::: ##.... ##::::... ##..::::: ##:::: ##:::::
   ##:::: ##:::::'##:. ##::::: ##:::: ##::::::: ##::::::: ##:::: ##:::::
   ########:::::'##:::. ##:::: ########:::::::: ##::::::: #########:::::
   ##.....:::::: #########:::: ##.. ##::::::::: ##::::::: ##.... ##:::::
   ##::::::::::: ##.... ##:::: ##::. ##:::::::: ##::::::: ##:::: ##:::::
   ##::::::::::: ##:::: ##:::: ##:::. ##::::::: ##::::::: ##:::: ##:::::
  ..::::::::::::..:::::..:::::..:::::..::::::::..::::::::..:::::..:: """
  #----------FASTIOSTART-----------#
  
  from __future__ import division, print_function
  import os
  import sys
  from io import BytesIO, IOBase
  if sys.version_info[0] < 3:
  	from __builtin__ import xrange as range
  	from future_builtins import ascii, filter, hex, map, oct, zip
  BUFSIZE = 8192
  class FastIO(IOBase):
  	newlines = 0
  	def __init__(self, file):
  		self._fd = file.fileno()
  		self.buffer = BytesIO()
  		self.writable = "x" in file.mode or "r" not in file.mode
  		self.write = self.buffer.write if self.writable else None
  	def read(self):
  		while True:
  			b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
  			if not b:
  				break
  			ptr = self.buffer.tell()
  			self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr)
  		self.newlines = 0
  		return self.buffer.read()
  	def readline(self):
  		while self.newlines == 0:
  			b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
  			self.newlines = b.count(b"\n") + (not b)
  			ptr = self.buffer.tell()
  			self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr)
  		self.newlines -= 1
  		return self.buffer.readline()
  	def flush(self):
  		if self.writable:
  			os.write(self._fd, self.buffer.getvalue())
  			self.buffer.truncate(0), self.buffer.seek(0)
  class IOWrapper(IOBase):
  	def __init__(self, file):
  		self.buffer = FastIO(file)
  		self.flush = self.buffer.flush
  		self.writable = self.buffer.writable
  		self.write = lambda s: self.buffer.write(s.encode("ascii"))
  		self.read = lambda: self.buffer.read().decode("ascii")
  		self.readline = lambda: self.buffer.readline().decode("ascii")
  def print(*args, **kwargs):
  	sep, file = kwargs.pop("sep", " "), kwargs.pop("file", sys.stdout)
  	at_start = True
  	for x in args:
  		if not at_start:
  			file.write(sep)
  		file.write(str(x))
  		at_start = False
  	file.write(kwargs.pop("end", "\n"))
  	if kwargs.pop("flush", False):
  		file.flush()
  if sys.version_info[0] < 3:
  	sys.stdin, sys.stdout = FastIO(sys.stdin), FastIO(sys.stdout)
  else:
  	sys.stdin, sys.stdout = IOWrapper(sys.stdin), IOWrapper(sys.stdout)
  input = lambda: sys.stdin.readline().rstrip("\r\n")
  
  #----------FASTIOFINISH----------#
  
  import collections,re,itertools,statistics,math
  from collections import *
  from itertools import * 
  from statistics import *
  from math import *
  from re import *
  mod=int(1e9+7)
  imin=-2147483648;
  imax=2147483647;
  true=True
  false=False
  none=None
  inp = lambda : input()
  I   = lambda : int(inp())
  M   = lambda : map(int,inp().split())
  L   = lambda : list(M())
  Yes = lambda : print("Yes")
  No  = lambda : print("No")
  YES = lambda : print("YES")
  NO  = lambda : print("NO")
  chartonum={"1":1,"2":2,"3":3,"4":4,"5":5,"6":6,"7":7,"8":8,"9":9,"0":0}
  def IO(controll):
  	if controll==false:
  		sys.stdin = open('input.txt', 'r')
  		sys.stdout = open('output.txt', 'w')
  	else:
  		pass
  def true_yes(statement):
  	return YES() if statement else NO()
  def state(statement,one,two):
  	print(one if statement else two)
  def swap(a,b):
  	a,b=b,a
  def debug(something):
  	print(*something)
  def prec(a):
  	return ("{0:.9f}".format(a))
  def binary_search(arr,low,high,x):
  	while (low <= high):
  		mid=low+(high-low)//2;
  		if(arr[mid]==x):
  			return [mid,true]
  		elif(arr[mid] > x):
  			high=mid-1;
  		else:
  			low=mid-1;
  	return [-1,false]
  #----------TOTKA-----------#
  
  def kabraji_ka_totka():
  	# totka hai dosto !
  	IO(1)
  	for i in range(I()):
  		n=I()
  		arr=L()
  		arr.sort()
  		sum=0
  		for i in range(n-1):
  			sum+=arr[i]
  		res=arr[n-1]+(float(float(sum)/(n-1)))
  		print(prec(res))
  
  #----------TOTKA----------#
  
  if __name__=="__main__":
  	kabraji_ka_totka()
  