Your starting information should include the differant values of variable 'x' and the corresponding probabilities 'p(x)'. The sum of p(x) should equal 1.


x p(x)
0 .6
1 .2
2 .1
3 .1

The formula for finding the standard deviation of these values is σ = √(Σx2P(x)-μ2)

To enter this information into a graphing calculator, do the following:

  1. Go to STAT>EDIT>Edit
  2. Enter the values of x in the L1 column, and the values for p(x) in the L2 column
  3. Label the L3 column as L1^2. This will give you x2
  4. Label the L4 column as L2*L3. This will give you x2P(x)
  5. Label the L5 column as L1*L2. This will give you xP(x)
  6. Return to the home screen.
  7. Go to LIST(2nd-STAT)>MATH>sum(
  8. Enter the equation sum(L4)'. Record this value as Σx2P(x)
  9. 'Enter the equation sum(L5). Record this value as μ
  10. Enter the equation √(Σx2P(x)-μ2), substituting the variable with the previously recorded amounts
  11. The resulting value will be your standard deviation
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