The wear out of a machine is normally distributed with 90 percent of the failures occurring between 200 and 270 hr of use (i.e. 5 percent below 200 and 5 percent above 270 hr).
(a) Find the MTTF and the standard deviation of failure times.
(b) What is the reliability if the part is to be used for 210 hr and then replaced?
(c) Determine the design life if no more than a 1 percent probability of failure prior to replacement is to be tolerated.