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Normal Distributions and the 68-95-99.7 Rule and Quiz 2.1 Review AP Statistics Properties of The Normal Curve • • • • density curve Symmetric single peaked bell shaped. The 68-95-99.7 Rule (Also called the Empirical Rule) • In the normal distribution with mean and standard deviation • 68% of the observations fall within of the mean • 95% of the observations fall within 2 of the mean • 99.7% of the observations fall within 3 of the mean 2.8 page 89 IQ Scores Scores on the Wechsler Adult intelligence Scale (WAIS, a standard IQ test”) for the 20 to 34 age group are approximately normally distributed with =110 and =25. Use the 68-95-99.7 rule to answer these questions… • About what percent of people in this age group have scores above 110? • 50% • About what percent have scores above 160? • 2.5% • In what range do the middle 95% of all IQ scores lie? • 110 50 Quiz Review • Know the properties of a density curve and be able to tell if a given curve is a density curve (you may have to use basic rules for area of a rectangle and area of a triangle) • Know the properties of a normal distribution • Know the 68-95-99.7 (Empirical Rule) and how to apply it.