Suppose your Mars mission has two transport vehicles that you have to use for emergency rescue operations. The vehicles are of different designs (had different intended usages) and the engineers estimate that one will have an estimated life of 100 hours, the other will have an estimated life of 200 hours. Both vehicles are placed into service immediately and will be used until failure.

i. What is the probability that at last one of the vehicles will still be operational after 250 hours?