From the same poll as in Exercise 9, marketers want to know about the differences in use of the Internet by income.

Of 2741 who reported earning less than $50,000 a year, 1813 said they used the Internet. Of the 2353 people who reported earnings of $50,000 a year or more, 2201 said they used the Internet.

a) Find the proportions of those earning at least $50,000 a year and those earning less than $50,000 a year who said they use the Internet.

b) What is the difference in proportions?

c) What is the standard error of the difference?

d) Find a 95% confidence interval for the difference in the proportion of people who use the Internet between the two income groups.