Pow research center is a nonpartisan polling organization that provides information about issues, attitudes, and trends shaping america. in a recent poll, pew researchers found that 47% of american adult respondents reported getting at least some local news on their cell phone or tablet computer (pew research website, may 14, 2011). further findings show that 42% of respondents who own cell phones or tablet computers use those devices to check local weather reports and 37% use the devices to find local restaurants or other businesses.
do you think the pew researchers conducted a census or a sample survey to obtain their results? why?

Remember that the difference between census and a sample survey is that in a census you take all the people of population in consideration in the study, and in the sample survey you take a part of that population in consideration to survey.

SO here if you check the problem it says that "in a recent poll, Pew reserchers found that 47% OF AMERICAN ADULT RESPONDENTS"

that is the population of the study that you want to focus, but there are a billion of american adult in US right? so its impossible that this company Pow Research made a census if you consider that a billion of people in US is almost infinite number for a company with a finite number of employees.

Also remember that a company has a budget to consider every month or every year, so to make a census or a sample survey it takes time and money, just to survey 10 people in a streeth of US cost money so if you want to reduce cost you might need to do a sample survey instead of a census.

probability for j is 1/4

while

a is 1/6