Can you answer this moral question? (just saw this problem on tv)

Situation 1:
A train is approaching. 4 People are working on the railway, which will surely be killed by the train.
However, there is a switch, which you have control over, which would steer the train on another rail and save the 4 workers. However, another man is working on this rail, who would be surely killed by the train if you engage the switch.
These are your only options: engage the switch or do not engage the switch. You are unable to warn either party.

Situation 2:
A train is approaching. 4 People are working on the railway, which will surely be killed by the train. However, there is a bridge before them. On the bridge there is a fat man, which is so fat that he would stop the train and save the 4 workers.
But to achieve this, you would personally have to push him off the bridge and thus kill him.
These are your only options: Push the fat man off the bridge and save the workers and kill the man, or do nothing, and let the 4 men die. You are unable to warn the 4 workers.

How do you decide in each situation, and what is the reason for your decision, especially if they are different for each situation, in light of the fact that the outcome would be the same?