Suppose events E and F are disjoint. What is P(E and F)?

Variation of sample mean: With a population standard deviation of σ , the variation of the sample means is σX´ , which the standard deviation of the sample mean: σX= σ √n But if we don’t know the population standard deviation, σ , we use the sample standard deviation, S, to approximate the population standard deviation, and the variation of sample means becomes the standard error of the sample mean: S SEX= √ n In general, as long as outcomes of each trial are independent and from a fixed population (random & no replacement or large population relative to sample), then variation of sample ratio is inversely proportional to square root of sample size: squareroot of sample¿¿ std .dev.of individual measurements standard deviationof sampleratio= ¿