The first part I can do no problem! The second part... well I've really no idea what to do with that S term, I assume it has something to do with the strong law of large numbers? (w is an element in the set of outcomes) Borel-Cantelli Lemmas Law of Large Numbers Does anyone know where to start? Thanks edit: I have an exmple of strong convergence showing that if P(w : lim Xn(w) = X(w) ) then this is identically equal to P(Xn -> X) = 1 , almost surely So I guess I just have to show that P(Xn -> X) = 1, So show: P(Sn(w)/n -> -1) = 1? Probably going the wrong way around it.. not sure how Borel Cantelli links to it.