A normally distributed variable, x, has a standard deviation of 3.9. Also, 71.37% of the data are larger than 249.8. Find the mean of x.

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.