STT 201 Chapter 8 Random Variables X discrete random variable K a number that the discrete random variable could assume P x k the probability that x k Empirical Rule applies to any normal curve o 68 fall within 1 Standard Deviation S D o 95 fall within 2 S D s o 99 7 fall within 3 S D s z score measures the number of standard deviations that a value falls from the mean z o z value mean standard deviation o positive z value is above the mean o negative z value is below the mean Binomial Distribution conditions o Has 2 possible outcomes success v failure o Each trial has same probability of success success p faiure 1 p o Trials are independent of each other o Number of trails are fixed Mean number of trials n probability p