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Sample size estimation

A) A nutritionist wants to estimate the mean amount of cholesterol in a certain variety of chicken eggs. She wants to be within 14 mg. with 99% confidence. It is believed that the standard deviation is 25 mg. How large a sample of eggs should she use?

B) A nurseryman wants to estimate how many poinsettias he will need for Christmas. He estimates the standard deviation to be 15. If he wishes to be 95% certain of having enough plants, how large a sample must he take to be within 5 plants?

C) The manager of a supermarket wants to estimate the proportion of customers who will be using food stamps at his store. How large a sample is required to estimate the true proportion to within 2% with 99% confidence?