Easy brain teasers and puzzles
Three players gamble on a “doubling game.” In each round of the game, a single loser is determined, and this player has to double the money of the other two.
After three rounds of this game, each player has lost one round each, and each player now has $24.
How much money did each player start with?
You drink half a cup of water. Then I drink half of what is left.
Then you drink half of what is left after that, and I drink half of what is left after you drink.
This continues until the cup of water is all gone.
What proportion of the cup of water did you drink by the end?
A detective is called upon to solve the riddle of the mystery killer in a high-profile murder.
There are only three suspects:
The victim was holding a calendar, and it seems he marked several of dates before he passed away: the second of January, the sixth of February, the third of April, the fourth of October, and the first of November.
With this information, the detective identified the culprit. Who was it?
Ava, Beth, Cam, and Derek each have a different favorite fruit and favorite color. We know their favorite fruits are apple, banana, cherry, and durian, and their favorite colors are blue, green, red, and yellow. We also know:
What is each person’s favorite fruit and favorite color?
Move exactly 2 matches to make this a valid equation.
Bonus: find more than one solution.
In matchstick equation puzzles, you are not allowed to make an inequality symbol such as ≠, ≥, >, <, or ≤. That would make it too easy!
If a triangle has two sides with lengths 3 and 4, what should the length of the third side be in order to maximize the area of the triangle?
Compound words are words that are composed of two or more other words, like high + light = highlight.
Can you make compound words out of the following three words by adding the same 4-letter word either before or after each word?
What is the most frequent digit among the numbers between 1 and 1000 (inclusive)? Consider only base-10 whole numbers.
Suppose there is a game in which you roll a fair, 6-sided die and win dollars equal to the outcome of the roll. How much would you expect to win on average?
Suppose, if you don’t like the outcome of the roll, you can reroll the die once, and win dollars equal to the outcome of the 2nd roll (once you choose to reroll, you can no longer go back to the 1st roll). How much would you expect to win on average?
Suppose, if you don’t like the outcome of the 2nd roll, you can reroll the die once more, and win dollars equal to the outcome of the 3rd roll (once you choose to reroll, you can no longer go back to previous rolls). How much would you expect to win on average?
This was an actual brain teaser question once asked at Jane Street for an interview for an intern role.
