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. Since then, much effort has gone into monitoring PCB concentrations in waterways. Assume that water samples are being drawn from a waterway in order to estimate the PCB concentration. a) Suppose that a random sample of size 80 has a sample mean of 1.69 ppb and a sample standard deviation of 0.25 ppb. Find a 95% confidence interval for the PCB concentration. b) Estimate the sample size needed so that a 95% confidence interval will specify the population mean to within ±0.02 ppb.
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. Since then, much
effort has gone into monitoring PCB concentrations in waterways. Assume that water
samples are being drawn from a waterway in order to estimate the PCB concentration.
a) Suppose that a random sample of size 80 has a sample
standard deviation of 0.25 ppb. Find a 95% confidence interval for the PCB concentration.
b) Estimate the
population mean to within ±0.02 ppb.
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