During the recent century, some valleys in West Virginia have become heavily industrial. The industries that operate there emit pollution that can change the level of acidity (measured as pH level) of...

During the recent century, some valleys in West Virginia have become heavily industrial. The industries that operate there emit pollution that can change the level of acidity (measured as pH level) of rainwater that falls in the region. Scientists know that before industrial development of the region, the rainwater falling in that region had an average pH level of 6.3, with standard deviation 0.45. Recently, a study of rainwater collected in the region involved 39 samples of rainwater. The scientists observed a sample mean pH of 6.1.

1. 
   

   Can scientists conclude at the 1% level of significance that the average pH level for rain in this region is lower now than it was before heavy industry arrived?
   

   
   


2. 
   

   Calculate a 98% confidence interval for?. Does this support your result in part a? Why or why not?
   

   
   


3. 
   

   If the data claimed the average pH level was different now than it was before heavy industry, how would that change the p-value? Would this result in stronger or weaker evidence than the evidence of part a? Explain your answer.
   

   
   


4. 
   

   Would the evidence in part a be stronger or weaker if the sample size were increased, assuming everything else remained the same? Explain your answer.