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Unformatted text preview: E(X) x 12 b Chapter 6 A practical problem is that, for the normal distribution, there is no mathematical formula for computing cumulative probabilities. A quick solution is that computer software offers high accuracy methods for calculating probabilities. With Microsoft Excel normal distribution probabilities can be obtained by selecting Insert Function NORMDIST. The general usage is: NORMDIST(x, μ X , σ X , cumulative) where cumulative = 0 for the PDF, cumulative = 1 for the CDF 13 Chapter 6 Working with the Normal Distribution Before the days of high speed laptop computers, applied workers used statistical tables (printed in the Appendix to statistical textbooks) to look‐up normal distribution probabilities. Working with the statistical tables can be useful as a learning exercise as it gives emphasis to understanding the properties of the normal distribution. Therefore, as a check on the calculations that can be obtained with Microsoft Excel, the use of the normal distribution tables will be described here. It can be noted that probabilities depend on the setting of μ X and σ X , the mean and standard deviation of the random variable. However, it turns out that probabilities for the standard normal random variable Z with mean 0 and variance 1 can be used to calculate probabilities for any other normal distribution. The course textbook prints two versions of a table for the cu...
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