int main()
{
	int n,ge[100];
	double shu[100][1000],pingjun[100]={0},s[100]={0};
	int i,j;
	scanf("%d",&n);
	for(i=0;i<n;i++)
	{
		scanf("%d",&ge[i]);
		for(j=0;j<ge[i];j++)
		{
			scanf("%lf",&shu[i][j]);
			pingjun[i]+=shu[i][j]/ge[i];
		}
	}
	for(i=0;i<n;i++)
	{
		for(j=0;j<ge[i];j++)
		{
			s[i]+=pow((shu[i][j]-pingjun[i]),2)/ge[i];
		}
		printf("%.5lf\n",sqrt(s[i]));
	}
	return 0;
}
