Chapter 3, Section 2, Exercise 054 Number of Text Messages a Day A random sample

Question

Chapter 3, Section 2, Exercise 054 Number of Text Messages a Day A random sample of n=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(Overscript bar EndScripts)= (exact number, no tolerance) (b) Find a 95 % confidence interval for the mean number of text messages. The 95 % confidence interval is... to... .

Explanation / Answer

best estimate of population parameter. x =41.5

b) for 95% confidence interval ; z=1.96

std error of mean =std error/(n)1/2  =0.222

hence confidence interval =estimated mean -/+ z*Std error of mean =41.065 ; 41.935

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