Reinforced concrete beams are used in bridges. However, cracks develop in these beams and it has an accumulation effect over time. The time to failure of such bridges, in days, is modeled by a lognormal distribution, where the mean of the natural logarithm of the failure time is 7.6, with a standard deviation of 2.
(a) Find the mean life of beams.
(b) What is the standard deviation of the life of beams?
(c) Find the probability of a beam lasting more than 4000 days.