Consider a device that follows the Weibull lifetime distribution with parameters n$=9\mathrm{.}0$ years and B$=2.$

A preventive replacement policy is to be followed.

The policy says that preventive replacements are made at fixed calendar time intervals while failure replacements are done whenever needed. The interval policy is considered. Find the optimal preventive replacement interval X by minimizing

the unit time total cost when Cp $=$ $$1400$ and Cf $=$

$$5000.$ Feel free to use Matlab, Excel or other software to do numerical calculations. Using the step size around $0\mathrm{.}3$~$0\mathrm{.}5$

$($e$.$g$.,$ tp$=0\mathrm{.}3,$ tp$=0\mathrm{.}6,$ tp$=0\mathrm{.}9,$ tp$=1\mathrm{.}2,...,)$ to find the optimal tp$*.$ Your answer needs to include one decimal place.

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