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TI-83 Discrete Random Variables Suppose that x ( L1 ) is the number of pets owned by a family and P(x) ( L2 ) is the corresponding probability. This represents a discrete probability distribution. Enter it as seen on the right. Mean of a Discrete Probability Distribution The mean is calculated by x Px . Therefore, highlight L3 and enter L1 * L2 as seen to the right. Pressing ENTER will perform the calculation as can be seen here. Now to calculate the mean we must sum the values in L3 . Press 2nd QUIT to go back to the home screen. Now press 2nd LIST and you should see the following display. Key over to MATH and down to 5: sum( as seen here and press ENTER. Enclose L3 in parentheses and press ENTER. This gives you the mean of the Discrete Probability Distribution. Standard Deviation of a Discrete Probability Distribution Use x 2 Px 2 to calculate the standard 2 deviation. Begin by creating L4 with L1 * L2 as seen to the right. After pressing ENTER L4 will appear as follows. Go back to the home screen and enter the command seen in the window to the right. Press ENTER and you will get the standard deviation.