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A man decided to take the trolley to work one day. Along the journey, he discovered that the trolley driver has stepped off the trolley, and now no one was driving it. Determined to reach work on time, the man decided to become the new trolley driver.

As the man approached the road where his office was, he realized that the trolley lacked automatic brakes, and moreover, if the manual brakes were released, then the trolley would resume full speed automatically.

Moreover, the end of the track was ahead, as was a crowd of people, many of whom would be killed (approximately 100), if he stepped off the trolley to go to work.

It would seem the man could simply stay on the trolley to keep it from going. However, the man's job is saving people's lives. If the man did not show up at work exactly on time, 95 people would die.

Furthermore, the doors to the trolley lock as long as the manual brakes are held, so he cannot simply ask a bystander to step on board to solve his dilemma.

How can the man solve his dilemma, and can it be done without anyone being killed? If not, should he let 100 people die who were not otherwise his responsibility, while saving the 95 which is part of his job; or should he let the 95 people die in order to save the 100 which were not his responsibility?

Lastly, whatever he does, all he has on board is a short piece of string, a tennis ball, and an unused bullet - all within reach. All of the windows are locked, and the doors will only open to allow him to exit, but cannot allow another person on.

How does he solve his dilemma?

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    $\begingroup$ 95 people die if he doesn't get to work exactly on time, and the guy uses public transit, and doesn't leave himself any extra time in case of weather, traffic, or evil Riddlers. Serves him right I say! $\endgroup$ – deep thought Feb 4 at 0:21
  • $\begingroup$ I am also wondering why a person with such a critical job only has a tennis ball, string and an unused bullet $\endgroup$ – Walkerbo Feb 4 at 9:46
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    $\begingroup$ @deepthought haha, upvote 4 u $\endgroup$ – Riddler Feb 5 at 0:17
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    $\begingroup$ @Walkerbo You'd be surprised what thing people carry who use public transportation... $\endgroup$ – Riddler Feb 5 at 0:17
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    $\begingroup$ @Riddler how the heck did he get on the trolley? If the brakes lock the doors...well...seems there's something off with the set-up of this problem. :) $\endgroup$ – Brandon_J Feb 5 at 15:32
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Since this is a lateral-thinking puzzle and not a moral discussion, I will not provide justification for my own moral choice in this matter, other than to say this: the puzzle makes it ambiguous whether the man is responsible for the 100 people on the tracks or not. In the first paragraph it says "Determined to reach work on time, the man decided to become the new trolley driver". If he truly chose to drive the trolley without a conductor, then he assumed all the responsibilities of the conductor at the moment he made that choice, so all the 100 people on the tracks actually are his responsibility. Since the puzzle later states that he is not responsible for these people then I'll assume that he saw a trolley rolling by and just jumped on it and didn't realize there was no conductor until his stop. In this case the 100 people are not his responsibility.

Having said that, he can:

Save everyone.
While listing the only items he has on board is meant to exclude things like cell-phones and the like, it still doesn't address the man's clothes. I assume he wasn't naked on the train? In this case he'll have shoes, laces, pants, a shirt, etc. - plenty of material to rig up something to keep the manual break engaged. If the break is anything like a car, you can put a shoe on top of it while simultaneously jamming the same show under the gas pedal, that should hold it. If it's a hand break you can tie it off with your laces or shirt. If it's a button you can jam a shirt button or a piece of cloth into the space between the button and the housing to create enough friction for the button to stay pressed.
After he secures the breaks he can move around the trolley and the most obvious thing to do now is just break a window. He can now climb out and go to work.

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You know what I would do?

Put the trolley at its lowest speed, throw it in reverse, and get off.
Now it's someone else's problem.

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  • $\begingroup$ (Rot13)Vs gur trneobk unf arhgeny naq/be cnex frggvatf gurl zvtug or orggre pubvprf guna erirefr. $\endgroup$ – Matthew Barber Feb 5 at 23:27
  • $\begingroup$ @MatthewBarber I decided to look up what is obviously a cipher but that I had not seen before, very clever; and (Rot47)xV> :?4=:?65 E@ 28C66 H:E9 J@F $\endgroup$ – Riddler Feb 10 at 21:03
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He can save everyone!

He is the only person on the trolley. His office is a trolley control booth. His regular job is to pull a lever in the booth that switches the trolley to a new track. To save everyone, he gets off the trolley and pulls the lever, changing the trolley’s route and directing it away from the “approximately 100” people at the end of the line. The “approximate” number of people is actually exactly 95. Those are the 95 people he saves by doing his job.

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    $\begingroup$ I liked your thoughts $\endgroup$ – Riddler Feb 10 at 21:00
  • $\begingroup$ So far I liked yuour answer best, but I am awaiting something different since it wasn't the actual scenario. Keep lateral-thinking! @generalcrispy's answer was amusing, but unethical. Lol $\endgroup$ – Riddler Feb 11 at 23:05
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Answer 1:

Tie the tennis ball and bullet to the brake pedal using the string such that it is held down. He can then get off and the trolley will remain stopped.

Answer 2:

It never says he was the only passenger on the trolley, just that there was no driver. Therefore he could ask another passenger who didn't have a time critical job to become the brake holder.

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    $\begingroup$ "the doors to the trolley lock as long as the manual brakes are held" ==> he cannot exit the vehicle when the brakes are held. $\endgroup$ – Hugh Feb 5 at 20:10
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    $\begingroup$ @Brandon_J "...all of the windows are locked..." $\endgroup$ – Hugh Feb 5 at 22:48
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    $\begingroup$ Having Chuck Norris with you was never ruled out @Hugh $\endgroup$ – Brandon_J Feb 5 at 22:49
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    $\begingroup$ @Brandon_J very funny :D. It is tagged lateral-thinking... maybe you're onto something! $\endgroup$ – Hugh Feb 5 at 23:02
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    $\begingroup$ @hugh maybe you're onto something! $\endgroup$ – Riddler Feb 11 at 23:08

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