Example. There are four cards with a number I on them, five cards with a number 2, and one card with a number 3 in a box and you choose one card from the box. Let X be the random variable representing the number on the chosen card. • The probability distribution can be represented as a table below: X Probability 1 P(X=1) = 4/10 = 2/5 2 P(X=2) = 5/10 = 1/2 3 %3D P(X=3) = 1/10 %3D • How would you answer to the question of what value of X you expect as the result? We answer this question with the weighted average of values of X, Er• P(x) We call it the mean or the expected value of X and denote it by µ or µx to specify the variable. Find the standard deviation of X of the example: • We also can ask about the distribution of the values of X considering their probabilities: what is the standard deviation of X? We find the standard deviation using the formula, νΣ- Ρ() and denote it by σ or Σχ. Find the standard deviation of X of the example: 2.