The lifetime (in days) of a certain electronic component that operates in a high-temperature environment is log normally distributed with µ = 1.2 and ? = 0.4.
a. Find the mean lifetime.
b. Find the probability that a component lasts between three and six days.
c. Find the median lifetime.
d. Find the 90th percentile of the lifetimes.
Let Y be the lifetime of the component.
(a) 
(b) P(3
The z-score of 1.0986 is (1.0986 ? 1.2)/0.4 = ?0.25.
The z-score of 1.7918 is (1.7918 ? 1.2)/0.4 = 1.48.
The area between z= ?0.25 and z= 1.48 is 0.9306 ? 0.4013 = 0.5293.
Therefore P(3
(c) 
(d) 
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