This isn't a riddle.
You are in a mine cart, Indiana Jones and all that, hurtling down a track. You discover that your brakes are broken. The cart is totally out of control and picking up speed. You are about to bail when you can see ahead that the track forks. One track leads to three workers maintaining the track. The other track leads to a single worker, toiling alone in a dead end. You jump to safety and land next to the switch that controls which track the cart will go down. There is no escape for any of the workers, strangers every one of them, ahead of you on either track. Which track do you send the cart down?
You are working in a mine and you spot a cart full of ore rolling out of control down a track. (Stay the hell away from mine carts!) Three workers are ahead of the cart, oblivious to the lethal threat. The workers will surely die. You are standing behind a stranger who is also watching the tragedy unfold. You realise that if you pushed this stranger onto the track, the cart would be derailed and the three workers would be spared but the stranger would certainly be killed. Do you push the stranger onto the track?
Taken from an article in Discover Magazine