A company that advertises on the Web wants to know which search engine its customers prefer as their primary search engine: Google or Bing. Specifically, the company wants to know whether the preference depends on the browser being used. The file P08_28.xlsx contains counts of 800 customers' favorite search engine, broken down by the browser used.
a. Find a 95% confidence interval for the difference between two proportions: the proportion of Internet Explorer users whose favorite search engine is Google and the similar proportion of Firefox users.
b. Repeat part a, replacing Google with Bing.
c. Interpret the results in parts a and b. Do the search engine preferences seem to depend on the browser used?