This Logic Puzzle Is Stumping People All Over, So Can You Figure Out Which Of These Three Jellybeans Is Poisonous?
Some of you reading this may figure out which jellybean is poisonous without having to read the explanation. Most of you will not. However, if you see someone claiming that they figured it out because it was “simple” and “obvious” and “only an idiot couldn’t realize this shit,” that person is a liar.
How do I know they’re lying? Because someone who is smart enough to figure this out right off the bat is not stupid enough to waste their time commenting on Internet articles. Also, because this puzzle is fairly difficult. Originally posted to waitbutwhy, the story starts with you getting in trouble for stealing a plum. This is unimportant, but I’m including it anyway because I fucking feel like it. Punishment for stealing said plum is death, however rather than being bludgeoned with a tree stump or glocked in the face, you have the chance to save yourself:
He [old man you stole a plum from, you dirty, dirty asshole] takes you with him over to a tree stump and asks you to sit down next to the stump. He reaches in his pocket and takes out three jelly beans—a green one, a red one, and a blue one. He sits down on the other side of the stump and puts the three jelly beans on the stump in a row.
He says, “Here’s some good news. The way we do the death penalty here is that you have a chance to get out of it. Here’s the deal: Two of the jelly beans on the stump are poisonous—you’ll die within 30 seconds of eating either one of them. But one of the jelly beans isn’t poisonous and won’t harm you at all. All three of the jelly beans are delicious. The situation works like this: You pick one of the jelly beans and eat it, and if you happen to pick the non-poisonous one, you’re free to go. Cool?”
Super cool. These jellybeans look delicious and I am very, very hungry. J. Camm yells at me when I take my full lunch break at 3:00, god forbid it keeps me from posting important clickbait about Courtney Stodden.
Here are your options, again, in case you somehow neglected to notice the exact same photo at the top of this page:
Which one do you pick: green, red or blue?
Did you pick red or blue? Well that was WRONG! You picked green, as our anonymous narrator continues:
Before you put it in your mouth, the man stops you and says, “Wait a minute—there’s one other little tradition we have that we do with each prisoner. Hold on to your jelly bean. I’m going to remove one of the other two jelly beans and put it back in my pocket, and I’m going to remove a poisonous one. I know which colors are poisonous and which aren’t, and one thing I can tell you is that blue jelly beans are poisonous.”
He takes the blue jelly bean and puts it back in his pocket. That leaves the red jelly bean still on the stump and the green jelly bean still in your hand.
So what do you do: switch to the red jelly bean, or stick with the green one in your hand?
If you’re stumped like I was, here’s a quick little clip from the movie 21 that should help with your decision:
Did that change your decision at all? Yes? No? Well it should have, and here’s why via waitbutwhy:
When you initially picked the green jelly bean, there was a 1/3 chance that it was the safe one to eat, and a 2/3 chance that it was poisonous and the safe one was still on the stump. When the man removed a poisonous blue jelly bean from the stump, it told you no new info about the green jelly bean in your hand—that still had a 1/3 chance of being safe. But removing the blue jelly bean told you a lot about the red jelly bean—it told you that if the safe jelly bean had been on the stump, the red one is safe.
Put another way, if you picked a poisonous jelly bean—which you would do two-thirds of the time—then choosing to switch after he removes one will save you every time. If you picked the safe one to start off with—which happens one-third of the time—then switching will kill you. So switching is a good choice two-thirds of the time.
If you died, don’t feel bad — most of your friends and family are probably dead too. If you’re alive, then that also blows — as like I said, most of your friends and family are probably dead too.