Of the 1,000 students in a local college, 420 own brand x mobile phones and 580 own brand y mobile phones. of these students, 80 own both brands of mobile phones. find the probability that a student chosen at random has a brand x mobile phone given that he has a brand y mobile phone.

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.