For the formula, does anyone know what x and n stand for? I looked for the formula for standard deviation online, and it seems different from the one posted on the problem. Any help would be appreciated.

Also pointing out that formulas you find online assume you already have the entire dataset. In our case, we won't know all of the values until after they are entered. Our formula allows you to compute the cumulative parts of the formula while the user is still entering data.