#include #include #include using namespace std; #define N 305 int a[N],cnt[N]; double ans; int n,i,T; int main(){ scanf("%d",&T); while (T--){ scanf("%d",&n); memset(cnt,0,sizeof(cnt)); for (i=1;i<=n;i++){ scanf("%d",&a[i]); cnt[a[i]]++; } ans=0; for (i=1;i<=n;i++){ ans+=n-cnt[a[i]]; } ans/=4; ans/=(n*(n-1))/2; printf("%.6f\n",ans); } return 0; }