The life of semiconductor laser at constant power is normally distributed with mean of 7000 hours and standard deviation of 600 hours.
i. Determine the probability that a laser fails before 5000 hours?
ii. Determine the life in hours that 95% of the lasers exceed?
iii. If three lasers are used in a product and they are assumed to fail independently, what is the probability that all three are still operating after 7000 hours?