The output from a sewage treatment plant is constantly monitored to assess treatment efficacy. Suppose that the mean coliform content is 20 bacteria/ml with a standard deviation of 4 bacteria/ml. An automatic measuring device is being used to monitor the bacterial levels. An alarm should ring whenever the bacterial level exceeds the 97.5th percentile. The upper bound should be:
- 16 per ml.
- 20 per ml.
- 24 per ml.
- 28 per ml.
- 32 per ml.