10 riddles you can only solve if you're really smart

These riddles aren't for the weak.

They're certainly not the first puzzles of their kind to stump the internet, but they're sure to give your brain a workout.

Here are 10 tough riddles that you might be able to get right on your first try if you really know what you're doing.

"Einstein's Riddle" asks a simple question: Who owns the fish?

Legend has it that Albert Einstein made up this riddle when he was a kid.

Five houses painted five different colors stand in a row. One person of a different nationality lives in each house. The five home owners all drink some type of beverage, smoke a certain cigar brand, and have a certain kind of pet. But none of the owners drink the same beverage, smoke the same type of cigar, or have the same pet.

Using the 15 clues above, can you figure out who owns the fish?

Solving the riddle is as simple as mapping out the variables. Our sister site Business Insider has a full explanation of the answer.

Can you figure out the answer to the fourth equation?

The way to solve this is to figure out what numbers the symbols represent.

Start with the first equation: three shoe symbols added together equals 30, meaning that the shoe symbol represents the number 10. 

Then 10 + C + C = 20, so each cat represents the number 5.

Watch out though — not all of the cats are the same.

You can read a full explanation of how to solve the riddle from Reader's Digest here.

Which cup would be filled with coffee first?

If you look closely, you can see that all of the pipes in the image are blocked except for the ones leading to cup number five.