A system has a large number of components of the same type.
Assume that the failure time T (measured in hours) of any of these
components follows approximately a normal distribution, with mean
100 and standard deviation 20. Using this approximation, answer the
following questions.
a) To obtain the probability that a randomly selected component
lasts more than 115 hours, the standardized value is Z= ? ; thus,
the probability sought is: ?
b) It is desired to give a replacement warranty for any
component that lasts less than M hours. Find the value of M so that
the probability of the warranty being honored is only
3%.
c) If a random sample of 80 components of the same type is
selected, what is the mean expected sample failure time : and its
standard deviation.
standard deviation
. The probability that the sample mean time is at least 98 hours
would be: