A coal company wants to make a 95% confidence interval estimate for the mean daily tonnage of coal that they mine. The company reports that the daily output of coal ranges from 1200 to 1800 tons.

a. What is the planning value for the population standard deviation ()?

b. If the company desires a margin of error of 40 tons, what should the sample size be?

c. If the company would like the margin of error to be 50 tons, will the sample size need to increase or decrease?Why?