Number of Text Messages a Day A random sample of n=755n=755 US cell phone users age 18 and older in May 2011 found that the average number of text messages sent or received per day is 41.5 messages,¹ with standard error about 6.1. ¹Smith, A., "Americans and Text Messaging," Pew Research Center, http://www.pewinternet.org/Reports/2011/Cell-Phone-Texting-2011/Main-Report/How-Americans-Use-Text-Messaging.aspx, accessed September 19, 2011.

(a) Use the information from the sample to give the best estimate of the population parameter. x = 41.5

(b) Find a 95% confidence interval for the mean number of text messages. The 95% confidence interval is: