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Lecture Mar20

# Lecture Mar20 - Statistics for Business March 20th...

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Statistics for Business March 20 th Questions to be answered in lecture: What does the central limit theorem tell us? What is a Standard Normal RV? How can we come up with a 95% confidence interval for the population mean when the population standard deviation is known? A restatement of the Central Limit Theorem: Let (big) represent the random variable corresponding to the experiment of selecting a random sample (of size n>30) and computing the mean of that sample. will be a Normal Random Variable with the mean of the population ( ) the variance of the population divided by the sample size ( ) Example: Suppose it is known that the average lifetime of an iPhone 5S is 900 days, with a standard deviation of 200 days. If we monitor and record the lifetimes of a sample of 80 iPhones, (a) What is the probability that the mean of the sample is larger than 950 days? (b) What is the probability that the mean of the sample is between 875 and 900 days?

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Standard Normal RVs A Normal RV that has mean and variance
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