Contaminated water: Polychlorinated biphenyls (PCBs) are a group of synthetic oil-like chemicals that were at one time widely used as insulation in electrical equipment and were discharged into rivers. They were discovered to be a health hazard and were banned in the 1970s. Assume that water samples are being drawn from a river in order to estimate the PCB concentration. Suppose that a random sample of size 71 has a sample mean of 1.88 parts per billion (ppb). Assume the population standard deviation is a=0.35 ppb. Part: 0/3 Part 1 of 3 (a) Construct a 98% confidence interval for the PCB concentration. Use tables or technology. Round your answers to at least two decimal places. The confidence interval 00. 5