Three jelly beans are laid on a stump and you have to choose one to eat, but two of them are poisonous and will kill you. Photo / Waitbutwhy.com
You've found the hidden panda and sussed out the image contained in a seemingly solid red dot, but now there's a new head-scratching riddle sweeping the internet.
Tim Urban and Andrew Finn of the website butwaitwhy.com have created a fiendishly difficult puzzle based around three jelly beans.
The premise of the puzzle is that you have to choose to eat one of three jelly beans laid out on a stump, two of which are poisonous.
"Two of the jelly beans on the stump are poisonous-you'll die within 30 seconds of eating either one of them," the riddle explains.
"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."
According to the riddle, you decide to pick up the green jelly bean.
But just before you eat it, a man takes away the blue jelly bean explaining that it's definitely poisonous.
That leaves the red one on the stump and the green one still in your hand. You get one last chance to change your mind about which one to take.
Solving the riddle involves choosing between the red and green jelly beans - one of which is definitely poisonous.
You might think that now it's down to two jelly beans that there's a 50-50 chance you have the poisonous one and decide to stick with green.
In fact, it's twice as likely to poisonous and the red jelly bean is two thirds more likely to be safe.
"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," Tim Urban of Wait But Why explained.
"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."
The test is just the latest in a string of a popular brain teasers sweeping the net.
Recently, puzzlers were challenged to find a hidden picture inside a red circle?
The brain teaser was said to test the internet's vision with people able to see everything from a detailed image to just an outline, while others struggled to spot anything at all.
Try the test and find out what you can see (App users click here).
While some claimed they could see the whole image in perfect detail, others were left scratching their heads in confusion.
When the dot is flipped you can clearly see a detailed sketch of a horse complete with a mane and tail, saddle and bridle and grass around its feet.
Some people can only see the outline of the image before the red spot is flipped, while others say they can see much more. Try the test below to see how you get on.
An image of an iPhone screen became an internet sensation recently as thousands of people deliberated over the photo, which was widely shared along with the question: "How many threes can you see in this picture?"
Social networkers came up with the most common answers of either 15, 19 or 21. But which answer is correct?
There are in fact 19 number threes pictured in the image, but there could be 21 depending on how you interpret the question.
Apart from the eight threes in the phone number, there are two threes on the key pad as the number eight button has been replaced.
At 3.33pm, the time also contains three number threes and the battery power at 33 per cent contains another two.
That totals 15, the answer many social networkers have come to. On closer inspection, however, there are a further four hidden digits, totaling 19.
Three of the letters in the contact's name have been replaced with threes and the letter 'I' on the number four key has also been replaced.
But many online posts give the answer to be 21, with people seeming convinced that there are a further two threes in the image.
The differing opinions come down to the interpretation of the question. The images has been widely shared on Facebook and Twitter with the message. 'How many threes do you see in this picture?'
Many users have included the network bar and WiFi signal, both of which show three bars. But whether 19 or 21 is the correct answer is a matter of opinion.
The puzzle, which has been widely shared on Facebook and Twitter after resurfacing again online, has instigated heated debate - with many left flummoxed at how others arrive at a different answer.
Twitter user Dani posted: "This thing annoyed the hell out of me when someone said 21. I was like no there's 18 until I looked again properly haha."
Facebook Ravi Vidyadhar Pathak came to a grander total and said: "28 if it's saying to count everything that resembles to 3 including the network signal which is 3 dots the page info on left which is 3 the buttons having 3 letters ABC."
Another philosophical Facebook user Marc Joseph posted: "I see only 2....and technically am correct cause you never asked how many 3's are there in the pic."
Athene Whitfield finally concluded the answer was 19 but had made so many previous guesses she posted: "I got to that in the end but thought - I can't send an answer through again!!? Was getting embarrassed!"
One user by the name of Sarah was so involved in the problem she posted a mock-up of the screen with the potential answers highlighted in purple.
When a friend posted "Not sure where you get 20 from" she posted: "Now I'm not sure."
It follows an optical illusion poster featuring tigers that resurfaced online this week, asking viewers to guess how many animals it featured.
On close inspection the picture has the big cats hiding in the bushes, bark and even the sky.
The image, which appears to have been produced as a poster, has two adults tigers and their two cubs in the foreground.
After that it becomes trickier to track down the felines in the picture but there are 12 other tiger faces hidden.
In the foliage to the right of the tigers, there's a fern in the shape of a tiger's face, with two hiding in the dirt beneath the tigers' feet.
In the top of the picture, there are five feline faces hidden within the branches of the trees.
While another two are seen in the wide trunk of the tree on the left of the picture and another tiger is face is seen on the left behind it and the last one is hidden in the soil below.
The poster, which features 16 in total, appears to be aimed at children, like many of the logic puzzles which have stormed the internet recently.
Another recent brain teaser saw a children's picture with tourists at a holiday campsite and challenged them to answer a list of nine questions.
The image is thought to be from an old children's magazine, according to The Independent, but the tough questions are likely to also leave adults scratching their heads.
The black and white drawing showed three people at the campsite. One is standing by the cooking pot with a ladle, another is rifling through his backpack, and a third is taking photos.
A sign nailed to a tree states said: "On duty. Colin, 7. Peter, 8. James, 9". The final name is obscured, but the number 10 is visible.
A picnic blanket with four plates, four spoons and a watermelon is laid out on the ground and a hen is scratching in the grass nearby.
Nearby, a tent is pitched and a spider has built a cobweb between the edge of the tent and a nearby tree.
The first question asks how many people are staying at the camp.
They must also figure out whether they arrived that day or a few days earlier, how they got there and how far away the closest town is.
In addition, they are asked whether the wind is blowing from north or south and what time of day it is.
The next question is to state where someone called Alex went.
Finally, they must figure out who was on duty yesterday and what day of the week it is.
Unlike the many cartoons that have swept the web in recent months challenging users to spot figures hidden in a sea animals or Star Wars characters, this puzzle relies on deduction.
The answer to how many tourists there are is relatively easy to figure out.
As there are four spoons and plates on the blanket and four names on the duty list, the answer is quite obvious.
The cobweb gives a clue to when the group arrived as it must have been a few days earlier to give the spider time to build it.
An oar leaning up against the tree is the key to figuring out how they got there - by boat.
The hen indicates that the nearest town is not far away as it's managed to wander into the campsite.
A flag on the tent, known as a windsock, shows that the wind is blowing from the south, but to figure this out you need to be aware that branches on the southern side of trees in the UK get more sun and grow more densely.
To figure out the time, you need to use the previous answer which tells you south from north to figure out where is east and west and deduce the time based on shadows.
The answer is that it's morning because the boy by the cook pot's shadow extends to the west.
Because we're asked where Alex went, we can assume he's not visible in the picture. However a butterfly net can be seen behind the tent. So the answer is that he's gone to catch butterflies.
To figure out who was on duty yesterday first consider that Colin, Peter, James and Alex are staying at the camp.
We know that Alex is catching butterflies and the person taking photos must be James, as there's a tripod sticking out of the bag marked J.
The person looking through the backpack is Colin as it's marked with a C.
That means Peter must be the one standing by the cooking pot. If Peter is on duty today, then according to the list on the tree Colin was on duty yesterday.
Figuring out the day of the month isn't too tricky as according to the duty list it's the 8th of the month.
But establishing what month it is may prove rather more difficult. The solution lies in the watermelon on the picnic blanket.
The answer is August 8, but you would have to be aware that it's the month in which watermelons ripen to find the correct answer.
Its long list of questions makes the puzzle even more baffling than a challenge by Gergely Dudas who first drove the internet mad trying to find a panda among a group of snowmen, and a cat blended into rows of owls.
The Hungarian cartoonist posted his latest puzzle a few days ago to celebrate Easter, challenging fans to find an egg cleverly disguised alongside a group of bunnies.
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