In exercises that call for two-sample procedures, you may use either of the two approximations for the degrees of freedom that we have discussed: the value given by your software or the smaller of and . Be sure to state clearly which approximation you have used.

Question 7.54

7.54 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.

noise

  1. Construct a 95% confidence interval for the mean dB level in high-intensity classes.
  2. 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. Repeat parts (a) and (b) for low-intensity classes.
  4. Explain how one might use these intervals to determine the staff size of a new gym.