题目：传送门。
#include <iostream>
#include <algorithm>
#include <cstdio>
#include <cstring>
using namespace std;
int gcd(long long a,long long b)
{
if(!b) return a;
return gcd(b,a%b);
}
int a[];
int main() {
int T,n;
scanf("%d",&T);
while(T--) {
long long sum=;
scanf("%d",&n);
for(int i=;i<n;i++) {
scanf("%d",&a[i]);
if(a[i]<) a[i] = -a[i];
sum+=a[i];
}
long long ap = sum,aq = n;
long long g = gcd(n,sum);
ap = ap/g;
aq = aq/g;
//printf("%I64d/%I64d\n",ap,aq);
long long z=;
long long m=;
for(int i=;i<n;i++) {
z+=a[i]*a[i];
m+=*a[i];
}
long long p,q;
//p = ap*ap*n;
//q = aq*aq;
p = n*z-sum*sum;
q = n;
g = gcd(q,p);
p /= g;
q /= g; printf("%I64d/%I64d\n",p,q);
}
}