The quick method for a confidence interval for a proportion uses
as an approximation for a 95% confidence interval. The margin of error in this case is slightly larger than necessary. Suppose that a simple random sample of 500 motorcycle registrations finds that 68 of the motorcycles are Yamahas. Give a 95% confidence interval for the proportion of motorcycles in the population that are Yamahas using the quick method of chapter 3 and then by the more precise method of chapter 21.