Cave/Flashlight/Exercise

Stuck in a cave, there are four people at the end of the corridor. They have just one flashlight, and the corridor leading outside can only be tackled with the flashlight. At most two people can walk together through the corridor. The people have different levels of skills to walk through the corridor, the first person needs an hour, the second person needs two hours, the third person needs four hours and the fourth person needs five hours to pass the corridor. If two of them walk together, always the slower one determines the velocity.

1. Suppose that the battery of the flashlight works for exactly ${}13$ hours. Can the four leave the cave?
2. Suppose that the battery of the flashlight works for exactly ${}12$ hours. Can the four leave the cave?

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