Motorcycle Noise A recent study of 42 motorcycles found that the average noise pollution in decibels is 90 , If the population standard deviation is 39 decibels, find the 93% confidence interval for the mean. Round answers to the nearest whole decibel, Round intermedlate answers to two decimal places. We are 93% confident that the mean noise pollution level is between and decibels, based on a sample of 42 motorcycles