I came across this question in USABO 2013 open exam:
A mother antelope and its child are galloping along the plains, when they encounter a group of hungry lions. If the two antelopes try to escape the lions together, there is a 75% chance that both will be consumed and eaten, and a 25% chance that both will escape alive. If, however, the mother sacrifices herself to the lions, she may be able to buy her baby additional time to escape.
What is the minimum chance that the baby can have to escape from the lions following such a sacrifice such that the mother’s action will be evolutionarily favored?
You may assume that the baby antelope, once escaped, will be guaranteed to survive into a reproducing adult, and that the mother antelope is at the beginning of reproductive age.
I suppose one should use Hamilton's Rule ($r \cdot B > C$) to solve this issue. I'm not familiar with the working of this rule to put it into the question's context. To my understanding $r=0.5$ but this is pretty much how far I managed to go.