Most binomial probability calculations required in these exercises can be done by using Table C or the Normal approximation. Your instructor may request that you use the binomial probability formula or software. In exercises requiring the Normal approximation, you should use the continuity correction if you studied that topic.

Question 5.22

5.22 Checking smartphone.

A 2014 Bank of America survey of U.S. adults who own smartphones found that 35% of the respondents check their phones at least once an hour for each hour during the waking hours.6 Such smartphone owners are classified as “constant checkers.” Suppose you were to draw a random sample of 10 smartphone owners.

  1. The number in your sample who are constant checkers has a binomial distribution. What are and ?
  2. Use the binomial formula to find the probability that exactly two of the 10 are constant checkers in your sample.
  3. Use the binomial formula to find the probability that two or fewer are constant checkers in your sample.
  4. What is the mean number of owners in such samples who are constant checkers? What is the standard deviation?