Here's your hypothetical dilemma of the day:
You are alone in a room with two buttons. There is a room adjacent to yours, but there's no way for you to know who or what's in it. There are people in the other room, but they can't see you either.
The two buttons do this: One kills you, and lets everyone in the other room go free; the other kills everything in the other room, and you walk away unharmed. You must press one or the other, or everyone will die.
The question is not "Which button do you press?," but rather...
"How many people must be in the other room for you to choose to save them instead of yourself?"
You are alone, and no one will know it was your decision to make. (unless you choose to live, then choose to tell others later...) If you spare the people in the other room, they will never know they were spared. You will only know the number of individuals in the other room, not their identities. They could be strangers just as well as they could be friends and family.
So, how many?
Edit for emphasis