I learned this 4 months ago and now I forgot how to do it.....
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Answer: 95% confidence interval for the difference between the proportions would be (1.31, 1.39).
Step-by-step explanation:
Since we have given that
Number of alluvial wells = 349
Number of quaternary wells = 143
Number of alluvial wells that had concentrations above 0.1 = 182
Number of quaternary wells that had concentrations above 0.1 = 112
Average of alluvial wells = 0.27
Standard deviation = 0.4
Average of quaternary wells = 1.62
Standard deviation =1.70
So, 95% confidence interval gives
alpha = 5% level of significance.
So, 95% confidence interval becomes,
Hence, 95% confidence interval for the difference between the proportions would be (1.31, 1.39).