An advertising agent for a cereal company wants to know the age of people watching "fists of fury television" on saturday mornings. A random sample of 50 viewers showed an average age of 12.7 years. From previous experience it is known that std deviation of 2.9 years. Find a 90% confidence interval for the mean age of all viewers.

How large should our sample be if we want to be sure that our sample mean is within .5 years of the true population mean?

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