All of the equations, you are going to be given s1 and s2, all of the equations are going to want variables so the first thing you should do when you are given your data set is you have standard deviation is to square them for each one and cross these out because you are never going to use standard deviation in these equations, its always going to be variance and that's where a lot of mistakes are made in the equations is people plug in variance or their is too much stuff written down so just get rid of these right away and that's it 