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Read problems statements in Russian and Vietnamese as well.
Chefu is Chef's little brother, he is 12 years old and he is new to competitive programming.
Chefu is practicing very hard to become a very skilled competitive programmer and win gold medal in IOI.
Now Chefu is participating in a contest and the problem that he is trying to solve states:
Given an array A of N integers, find any i, j such that i < j and Ai + Aj is maximum possible
unfortunately, there's no much time left before the end of the contest, so Chefu doesn't have time to think of correct solution, so instead, he wrote a solution that selects a random pair (i, j) (i < j) and output Ai + Aj. each pair is equiprobable to be selected.
Now Chefu wants your help to calculate the probability that his solution will pass a particular input.
First line contains an integer T denoting the number of test-cases.
First line of each test-case contains a single integer N
Second line of each test-case contains N space-separated integers A1 A2 ... AN
For each test-case output a single line containing a single number denoting the probability that Chefu's solution to output a correct answer. your answer will be accepted if the absolute difference between it and correct answer is less than 1e-6
Input: 3 4 3 3 3 3 6 1 1 1 2 2 2 4 1 2 2 3 Output: 1.00000000 0.20000000 0.33333333
|Tags||cakewalk, cook88, kingofnumbers, kingofnumbers, likecs, probability|
|Time Limit:||1 sec|
|Source Limit:||50000 Bytes|
|Languages:||C, CPP14, JAVA, PYTH, PYTH 3.6, PYPY, CS2, PAS fpc, PAS gpc, RUBY, PHP, GO, NODEJS, HASK, rust, SCALA, swift, D, PERL, FORT, WSPC, ADA, CAML, ICK, BF, ASM, CLPS, PRLG, ICON, SCM qobi, PIKE, ST, NICE, LUA, BASH, NEM, LISP sbcl, LISP clisp, SCM guile, JS, ERL, TCL, kotlin, PERL6, TEXT, SCM chicken, CLOJ, COB, FS|
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