A simple random sample of 100 8th graders at a large suburban middle school indicated that 82% of them are involved with some type of after school activity. Find the 95% confidence interval that estimates the proportion of them that are involved in an after school activity. The gas mileage for a certain model of car is known to have a standard deviation of 4 mi/gallon. A simple random sample of 49 cars of this model is chosen and found to have a mean gas mileage of 27.5 mi/gallon. Construct a 96.5% confidence interval for the mean gas mileage for this car model.
A 95% confidence interval for the mean of a population is to be constructed and must be accurate to within 0.3 unit. A preliminary sample standard deviation is 1.5. The smallest sample size n that provides the desired accuracy is: