You have been hired by the Ford Motor Company to do market research, and you must estimate the percentage of household in which a vehicle is owned. How many households must you survey if you want to be 94% confident that your sample percentage has a margin of error of three percentage points

a) Assume that a previous study suggested that vehicles are owned in 86% of households.

b) Assume that there is no available information that can be used to estimate the percentage of

households in which a vehicle is owned.

c) Assume that instead of using randomly selected households, the sample data are obtained by asking

readers of the Washington Post newspaper to mail in a survey form. How valid are the results?