The article Occurrence and Distribution of Ammonium in Iowa Groundwater (K. Schilling, Water Environment Research, 2002:177186) describes measurements of ammonium concentrations (in mg/L) at a large number of wells in the state of Iowa. These included 349 alluvial wells and 143 quaternary wells. Of the alluvial wells, 182 had concentrations above 0.1, and 112 of the quaternary wells had concentrations above 0.1. Find a 95% confidence interval for the difference between the proportions of the two types of wells with concentrations above 0.1.

Statistics: Ch. 1 Important Definitions • Statistics—Numerical description of data • Population—A set of all subjects or elements about which we are interested in making inferences • Frame—A list containing all members of a...