Hi Tutu,

I think you know how to answer your own question, so I'm going to do my best to give you a hint without telling you what to do. You said,

But does have something to do with Stare at for a minute and I think you'll see what needs to happen.Isn't the variance the sum of ((xi-mean)^2) / n so it has nothing to do with the sum of (xi)^2?

Let me know if anything is unclear. Good luck!