3. Noise Levels in Hospitals The mean noise level of 20 randomly selected areas designated as "casualty doors" was 63.1 dBA, and the sample standard deviation is 4.1 dBA. The mean noise level for 24 randomly selected areas designated as operating theaters was 56.3 dBA, and the sample standard deviation was 7.5 dBA. At a = 0.05, can it be concluded that there is a difference in the means? 9. Find the 95% confidence interval for the difference of the means in Exercise 3 of this section.