Some consider Friday the 13th (any Friday that falls on the 13th day of a month) unlucky.
In a calendar year, how many Friday the 13th can occur? Find both the minimum and maximum.
Medium difficulty brain teasers and puzzles
Some consider Friday the 13th (any Friday that falls on the 13th day of a month) unlucky.
In a calendar year, how many Friday the 13th can occur? Find both the minimum and maximum.
Two ferry boats serve the same route on a river, but travel at different speeds. They depart from opposite ends of the river at the same time, meeting at a point 720 yards from the nearest shore.
When each boat reaches the other side, it takes 10 minutes to unload and load passengers, then begins the return trip. This time, the boats meet at a point 400 yards from the other shore.
How wide is the river?
The ferry boat problem is created by well-known puzzle author Sam Loyd.
Find a combination of three different positive integers x, y, and z such that:
x3 + y3 = z4
Hint: there’s a better way than brute force / trial & error.
These Wordle puzzles are nearly complete, you just need to finish them by figuring out the correct word. In each of these 5 puzzles, there should be just one or two valid answers remaining – find them!
Haven’t played Wordle before? You get 6 tries to guess the 5-letter English word, and for each guess you are shown whether each letter is in the right place in the word (green), in the word but in the wrong place (yellow), or not in the word at all (gray).
In the morbid game of Russian Roulette, a partially loaded revolver with a six-chamber cylinder is randomly spun, pointed at one of the players, and fired. If the revolver landed on an empty chamber, the lucky player is safe, and the process is repeated with the next player. The obvious objective of the game is to not get shot.
You find yourself stuck in a game of Russian Roulette. A freshly loaded revolver is aimed at the first player, and it turns out to be an empty chamber. Your turn is next, and you are given the choice to either:
Which choice should you pick if the revolver was originally:
Assume the revolver cannot misfire, and that spinning the cylinder lands on all chambers with equal probability.
Some variation of this Russian Roulette riddle was once asked in interviews at Jane Street, Susquehanna International Group (SIG), Facebook (now Meta), UBS, Capital One, and more.
Quick vocabulary puzzle – given the middle four letters of each word, figure out these 8-letter words:
Rearrange exactly 2 matches to make this a valid equation.
In matchstick math puzzles, you are not allowed to make an inequality symbol such as ≠, ≥, >, <, or ≤. That would make it too easy!
I like the numbers 4 and 5. I like to add 4’s and 5’s together to make other numbers, such as 4 + 4 + 5 + 5 + 5 = 23. How many numbers from 1 to 1000 can be written as the sum of 4’s and 5’s?
On a magical island, there are 100 lions and 1 sheep, all of which can live by eating the plentiful grass on the island. Any lion that eats the sheep will magically turn into a sheep afterward, such that there will always be a sheep on the island.
Every lion would like to eat a sheep, but would much rather prefer to not be eaten (they wouldn’t mind turning into a sheep if they wouldn’t be eaten).
If all the lions act rationally and know all the other lions act rationally, how many lions will remain on the island in the end?