The mean (or expected value) of a probability distribution can be calculated by first making the probability distribution. Then multiply the possible values of the Random Variable by their probabilities (X*P(X)) then add all the X*P(X) up. That gives you the mean. From there you need to find all the X2P(X) and add all those up. Then the standard deviation = X 2 P ( X ) ( X P ( X ) ) 2 On the TI 83/84 calculator you can 1) Enter the values of the RV's into List 1 (Press STAT, 1 (for Edit), highlight L1 and press CLEAR if needed, then enter values into the list) 2) Enter the probabilities into L2 (press > and then enter the values in the list. highlight L2 and press CLEAR first if needed). 3) 2nd MODE (to quit the list) 4) STAT, > (for CALC), select 1-Var Stats, List: L1 (2nd 1), FreqList: L2 (2nd 2). Then calculate. x is the standard deviation of the frequency distribution. Find the standard deviation X P(X) -3 0.6 6 0.4