8.26 According to the Investment Company Institute, 40% of U.S. households have an Individual Retirement Account (IRA). Assuming the population proportion to be  5 0.40 and that a simple random sample of 400 households has been selected: Source: Investment Company Institute, 2008 Investment Company Fact Book, p. 87.

a. What is the expected value of p 5 the proportion in the sample having an IRA?

b. What is the standard error of the sampling distribution of the proportion?

c. What is the probability that at least 35% of those in the sample will have an IRA?

d. What is the probability that between 38% and 45%

of those in the sample will have an IRA?