Solved: Let X denote the lifetime of a component, with

Chapter 4, Problem 122E

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Problem 122E

Let X denote the lifetime of a component, with f(x) and F(x) the pdf and cdf of X. The probability that the component fails in the interval . Dividing this by produces the failure rate function:

An increasing failure rate function indicates that older components are increasingly likely to wear out, whereas a decreasing failure rate is evidence of increasing reliability with age. In practice, a “bathtub-shaped” failure is often assumed.

a. If X is exponentially distributed, what is r(x)?

b. If X has a Weibull distribution with parameters α and β,what is r(x)? For what parameter values will r(x) be increasing? For what parameter values will r(x) decrease with x?

so that if a component lasts hours, it will last β forever (while seemingly unreasonable, this model can be used to study just “initial wearout”). What are the cdf and pdf of X?