Finding Minimum Probability


Below is the question in my homework. I don't know whether I've to solve this using Bayes' theorem or I have to provide a general answer.

"A mine pit has collapsed and 20 miners are stuck in an elevator under the mine pit. Since they are in the same elevator, assume we know that they are either all alive or all death. You need to decide whether to send in a rescue team or not. Since these attempts are dangerous, it is expected that on the average 5 rescuers to die if you send them to the mine pit. What should be the minimum probability of all miners being alive for it to be reasonable to send a rescue team? "

Kindly let me know should I say something like " probability of alive should be .95 percent" or I have to calculate. Thanks