# STAT 101 Chapter Notes - Chapter 3: Standard Deviation, Normal Distribution, Statistical Inference

## Document Summary

Density curves: density curve is. , always on or above the horizontal axis, never negatives, has area exactly 1 underneath it, are idealized patterns, symmetric, describes overall pattern of a distribution. Proportion of heads in many tosses of a coin: 3. many statistical inference procedures based on nd work well for other roughly symmetrical distribution, many income distributions are skewed to right. The 68-95-99. 7 rule: normal distribution w/ mean mu and sd sigma, approx 68% of observations fall within or mean , approx 95% of observations fall within 2 or , approx 99. 7% of obs. Fall withing 3 or ex) graph on pg 78; find the scores that 95% of all scores are between, and suppose that the mean is 6. 84 and sd is 1. 55. ~score 5. 69 is one standard deviation from mean (6. 84). 5. 29 8. 39 is 68%, meaning the the sum of the rest of the unshaded parts is 32.