7.60 Noise levels in fitness classes, continued. Refer to the previous exercise. In most countries, the workplace noise standard is 85 db (over eight hours). For every 3 dB increase above that, the amount of exposure time is halved. This means that the exposure time for a dB level of 91 is two hours and for a dB level of 94 it is one hour.

1. (a) Construct a 95% confidence interval for the mean dB level in high-intensity classes.

2. (b) Using the interval in part (a), construct a 95% confidence interval for the number of one-hour classes per day an instructor can teach before possibly risking hearing loss. (Hint: This is a linear transformation.)

3. (c) Repeat parts (a) and (b) for low-intensity classes.

4. (d) Explain how one might use these intervals to determine the staff size of a new gym.