The lifetimes of a certain type of electrical components are distributed with a
mean of 800 hours and standard deviation of 160 hours.
Required:
(i) Identify situation (2 marks)
(ii) If the manufacturer replaces all components that fail before the
guaranteed minimum life time of 600 hours, what percentage of the
components have to be replaced?
(3 marks)
(iii) If the manufacturer wishes to replace only 1% of the components that
have the shortest life, what value should be used as the guaranteed
lifetime? (3 marks)
(iv) What is the probability that the mean lifetime of a sample of 25 of these
electrical components exceeds 850 hours? (2
marks)