Question: A local newsletter is printed on a printer with a cartridge that may break or run out of ink during operation. The cartridges can be replaced for $7.50, but if they fail when the newsletter is being printed, the cost is estimated to be $25 because of the delay in publication. The failure distribution of the cartridges is
Weekof Use Probability of Failure
1 .1
2 .2
3 .3
4 .4
Determine the optimal time to replace the cartridges.