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7. The DENR sets a limit of 5 parts per million on PCB (a dangerous substance) in water. A major manufacturing firm producing PCB for electrical insulation discharges small amounts from the plant. The company management, attempting to control the amount of PCB in its discharge, has given instructions to halt production if the mean amount of PCB in the effluent exceeds 3 parts per million. A random sampling of 50 water specimens produced X = 3.1 parts per million and s = 0.5 parts per million. a. Do these statistics provide sufficient evidence to halt the production process at 1% level of significance? b. Construct a 99% confidence interval for u and compare your results with (a)