Determination of Sample Size.
A two-lane highway with a posted speed limit of 45 miles per hours is located just outside a small 40 homes subdivision. The residents of neighbourhood are concerned that the speed of cars on the highway is excessive and want an estimate of the population speed of the cars on the highway. Assume the population standard deviation speed of vehicles on the highway is known to be 8 miles per hour, based on past studies. How large a sample is required to approximation the mean speed with a margin of error equal to 2 miles per hour with 90 percent confidence?