According to a poll about phone use, 25% of all U. S. households are "wireless only," meaning they do not have a land Ilne. In a random sample of 15 households, what is the expected number of households that are wireless only?4
3.75
3
0.25

Monitors manufactured by tsi electronics have life spans that have a normal distribution with a standard deviation of 1800 hours and a mean life span of 20,000 hours. if a monitor is selected at random, find the probability that the life span of the monitor will be more than 17,659 hours. round your answer to four decimal places.