Version 1A trolley is headed toward a switch. As the switch is set, the trolley will go left and as a result will kill five people who are working (or tied to) the track. You can leave the switch as is or switch it to the right track. In that case it will kill a single person on the track.
Version 2You are standing on a bridge next to an obese person, watch the train approach. If it passes under the bridge it will kill five people on the track. You can save them only by pushing the large guy onto the track, thus resulting in his death.