How would you respond to a friend who asks you, “How can we say that the sample mean is...

How would you respond to a friend who asks you, “How can we say that the sample mean is a random variable when it is just a number, like the population mean? For example, in Example A of Section 7.3.2, a simple random sample of size 50 produced how can the number 938.5 be a random variable?”

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