Exam 17: Testing Hypotheses About Proportions

You want to see if the number of minutes cell phone users use each month has changed from its mean of 120 minutes 2 years ago.You take a random sample of 100 cell phone users and find an average of 135 minutes used.

The management of a water park has concerns about the chlorine level of 0.4% mg/mL increasing to an unsafe level.The management tests the hypothesis that the park's chlorine proportions have remained the same,and find a P-value of 0.005.Provide an appropriate conclusion

Marc wants to know if the mean age of the employees at his company is less than 26 years.He obtains a random sample of 100 employees,and finds a mean age of 25.1 years and a standard deviation of 9.2 years.

An airline's public relations department says that the airline rarely loses passengers' luggage.It further claims that on those occasions when luggage is lost,92% is recovered and delivered to its owner within 24 hours.A consumer group who surveyed a large number of air travelers found that only 145 out of 165 people who lost luggage on that airline were reunited with the missing items by the next day.Does this cast doubt on the airline's claim? Use a calculator to find z-scores and P-values.