Pew Research Center is a nonpartisan polling organization that provides information about issues, attitudes, and trends shaping America. In a poll, Pew researchers found that 73% of teens aged 13–17 have a smartphone, 15% have a basic phone and 12% have no phone. The study also asked the respondents how they communicated with their closest friend. Of those with a smartphone, 58% responded texting, 17% social media and 10% phone calls. Of those with no smartphone, 25% responded texting, 29% social media and 21% phone calls (Pew Research Center website, October 2015). 

a. One statistic (58%) concerned the use of texting to contact his/her closest friend, if the teen owns a smartphone. To what population is that applicable? 

b. Another statistic (25%) concerned the use of texting by those who do not own a smartphone. To what population is that applicable? 

c. Do you think the Pew researchers conducted a census or a sample survey to obtain their results? Why?