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Lesson 2.6 Normal Distributions: Finding original distribution. It is also possible to use technology to
Values from Areas find these values directly.
An unknown mean or standard deviation of a normal dis-
Values in a normal distribution that correspond to areas tribution can be found if the value of a percentile is known.
under the curve can be computed. A table of standard nor- First find the z-score that corresponds to the percentile,
mal probabilities (Table A) can be read backwards, going then plug in all the values except the unknown value into
from areas/probabilities to z-scores, while z-scores can be the formula for the z-score. Finally, algebra can be used to
obtained from areas directly by using technology. These solve for the unknown mean or standard deviation.
z-scores can then be “unstandardized” to give values in the

2-6 CHAPTER 2 • Modeling One-Variable Quantitative Data

03_TysonTEspa4e_25177_ch02_088_153_4pp.indd 6 10/11/20 7:41 PM