int main()
{
    int n,k,i,j;
    double x[100],a,b,c,d,s[100];
    scanf("%d\n",&k);
    for(j=1;j<=k;j++){s[j]=0;b=0;d=0;a=0;c=0;scanf("%d\n",&n);for(i=1;i<=n;i++){scanf("%lf",&x[i]);
    b+=x[i];}a=b/n;
    for(i=1;i<=n;i++){c+=(x[i]-a)*(x[i]-a);}d=c/n;s[j]=s[j]+sqrt(d);}
    for(j=1;j<=k;j++)
    printf("%.5lf\n",s[j]);
    return 0;
}