Can You Solve This Crazy Coffee Riddle?
Can You Solve This Crazy Coffee Riddle?

If you like riddles, you might have seen this puzzle sweeping across the internet. This riddle, which is a clever play on the field of fluid mechanics, shows a picture of four coffee cups, each connected to a pipe and container system at different depths and shapes. The fluid mechanic's riddle, originally posted to Twitter by @herbeautyxo, asks “Who gets the coffee first.”

You have probably seen variations of this riddle, usually using water tanks, several times before. For this reason, you might think that you can figure out the answer to this riddle relatively easy.

But with this riddle, you should take your time and really look at the problem. There are a number of deceiving tricks that make the most obvious answers incorrect. Before you go breaking out your college physics notes, you should know that the answer to the riddle is actually shockingly simple, and doesn’t require complex calculations or derivations.

The riddle itself is easy to understand. Coffee is poured into the top container in the image, flowing through a series of pipes to drip into the waiting coffee cups. The pipes, which are arranged in a maze of curves and junctures, dictate which cup gets coffee before the others. After uploading the riddle, @herbeautyxo wrote to her followers: “Let’s see who’s brain works. Who gets coffee first?”
The riddle quickly developed a high volume of tragic, garnering more than 5000 likes and over 2000 retweets. At the time of writing, more than 2000 people had commented on the tricky riddle, arguing about the best way to solve the problem.

Here are the assumptions you need to make in order to solve the coffee riddle.
The coffee is being poured into the top container at a constant rate.

There is enough coffee to completely fill the volume of unfilled space in the maze.

The most common answer given by Twitter users is that cup 4 receives the coffee first. This answer seems reasonable when you consider some of the basic principles of fluid mechanics. If this was correct, the next cup to receive coffee would by 9, then 7 and finally 5. However, the riddle’s creator has revealed that it is still incorrect, saying: “Nope, look closely.”

Another popular theory on Twitter was that each of the four cups would be filled at the same time, no matter the placement and shape of the pipe maze. This answer is absolutely untrue and can’t even be explained rationally.

Before we explain which cup it is, you might want to make yourself some coffee and have another look, the answer is right in front of you. Pay attention to the pipes themselves, not just the structure of the maze.

The only cup that gets the coffee is cup number 5. Every other cup has blocked junctures and openings in the pipe maze, ensuring that number 5 is the only cup to receive any liquid at all.



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