(3 points) The Highway Safety Department wants to study the driving habits of individuals. A sample of 35 cars traveling on a particular stretch of highway revealed an average speed of 69 miles per hour with a standard deviation of 6 miles per hour. Round to4 decimal places.
1. Calculate a 90% confidence interval for the true mean speed of all cars on this particular stretch of highway. ( 59.13 . 78.87 )
2. What sample size is needed to estimate the true average speed to within 1.5 mph at 90% confidence? Note: For consistency’s sake, round your t* value to 3 decimal places before calculating the necessary sample size.