When an opinion poll calls residential telephone numbers at random, only 23% of the calls reach a live person. You watch the random dialing machine make 18 calls.
What is the mean number (±0.1) of calls that reach a person?
What is the standard deviation ? (±0.001) of the count of calls that reach a person?
If calls are made to New York City rather than nationally, the probability that a call reaches a person is only p = 0.09.
What is the standard deviation (±0.0001) now?
What would be the standard deviation (±0.0001) if p = 0.0103?