The time between surface finish problems in a galvanizing
process is exponentially distributed with a mean a 40 hours. A single plant
operates three galvanizing lines that are assumed to operate independently.
a) What is the probability that none of the lines experience
a surface finish problems in 40 hours of operations?
b) What is the probability that all three lines experience a
surface finish problem between 20 and 40 hours of operation?
c) Why is the joint probability density function not needed
to answer the previous questions?





