8.79 Travel to work As part of the 2000 census, the Bureau of the Census surveyed 700,000 households to study transportation to work. It reported that 76.3% drove alone to work, 11.2% carpooled, 5.1% took mass transit, 3.2% worked at home, 0.4% bicycled, and 3.8% took other means.

a. With such a large survey, explain why the margin of error for any of these values is extremely small.

b. The survey also reported that the mean travel time to work was 24.3 minutes, compared to 22.4 minutes in 1990. Explain why this is not sufficient information to construct a confidence interval for the population mean. What else would you need?