As MugaSofer said, it doesn’t need be 400⁄500, it may be 400⁄1,000,000 vs (500/1,000,000 with 90% probability). The original question indicated “Suppose that a disease, or a monster, or a war, or something, is killing people. ”
Imagine that hundreds of thousand lives are getting lost.
If you leave out writing out that 100 people are dying, you’re also subtly encouraging your readers to forget about those people as well, so it comes as little surprise that some would prefer option 1.
How about the following rephrasing?
There’s a natural catastrophe (e.g. a tsunami) occuring that will claim >100,000 lives. You have two options:
Save 400 lives, with certainty.
Save 500 lives, 90% probability; save no lives, 10% probability.
As MugaSofer said, it doesn’t need be 400⁄500, it may be 400⁄1,000,000 vs (500/1,000,000 with 90% probability). The original question indicated “Suppose that a disease, or a monster, or a war, or something, is killing people. ”
Imagine that hundreds of thousand lives are getting lost.
How about the following rephrasing?
There’s a natural catastrophe (e.g. a tsunami) occuring that will claim >100,000 lives. You have two options:
Save 400 lives, with certainty.
Save 500 lives, 90% probability; save no lives, 10% probability.
I think that rephrasing improves it.