## 24 Game Puzzle

How do you use 3, 3, 8, and 8 to make 24? Each number must be used exactly once, and only addition, subtraction, multiplication, division, and parentheses can be used.

## 5 Pirates Puzzle

Five pirates are figuring out how to divide up a newly plundered treasure of 100 gold coins. From most senior to least senior: Pirate A, Pirate B, Pirate C, Pirate D, and Pirate E. The rules: The most senior pirate…

## Match Maximization

What is the biggest number you can make by moving exactly 2 matches in the number above? Assume that numbers must be represented in their standard “digital clock” font (for example, a “1” requires two segments).

## Wrong Seat Probability

There is a fully-booked flight with 100 seats. The first person decides to ignore the seat assignments, and sits in a random seat. Each subsequent person sits in their assigned seats if available, or sits in a random unoccupied seat…

## Solitary Word

I am a solitary word. If I lose my first letter, I remain the same. If I lose my first letter again, I still remain the same. What am I?

## Sword is Mightier than the Bow

Shot two arrows at its center and missed both times,swung a sword once at its center and hit twice.What is it?

## Card Pairing Game

You are playing a game with your friend using a standard deck of 52 playing cards. Each round, you flip over two cards: If both cards are black, you keep the cards and earn one point. If both cards are…

## Square in a Square

In the larger square, there is a smaller square formed by lines connecting each corner to the midpoint of one of the sides. Question: What fraction of the larger square is the smaller filled square?

## Base Rate Fallacy

What is the Base Rate Fallacy? In simple terms, it’s a common error we make in assessing likelihoods due to (a) over-emphasizing the rate of something within a group and (b) under-emphasizing how common that group is in the first…

## Nob’s Number Tree Puzzle

Nob’s Number Tree What number belongs in the “?” circle? Note that all numbers shown are correct, there are no typos or errors. Nob Yoshigahara’s Puzzles Nob’s Number Tree is a well-known brainteaser by the Japanese puzzle guru Nobuyuki “Nob”…

## Missing Dollar Riddle

The missing dollar riddle is a classic brain teaser that can trip up even savvy puzzle solvers: Three friends split the cost of a hotel room. They are charged \$30, so each of them pays \$10. Later the hotel manager…

## Divisible by 100

Prove that for any set of one hundred whole numbers, either one of those numbers is divisible by 100 or the sum of a subset of those numbers is divisible by 100.

## Throwing a Ball

When you throw a ball straight up, does it spend more time going up, more time coming down, or the same time going up and down – taking into account both gravity and air resistance?

## Chance of Rain

You are driving to Seattle to meet some friends, and want to know whether you should bring an umbrella. You call up 3 of your friends who live there and independently ask them if it’s raining. Your friends like to…

## Seven Times the Sum of Its Digits

Which two-digit numbers are exactly equal to seven times the sum of its digits?

## Pigeonhole Principle

The Pigeonhole Principle is a simple and elegant concept: If you place more than n pigeons into n pigeonholes, at least one of the pigeonholes must contain more than one pigeon. More generally, if you need to make more than…

## Slowing and Shrinking

Remove one letter from the word “SLOWING” to make another valid English word. Repeat this step until you are left with just one letter, ensuring every step results in an English word. What words did you make in the process?

## Game the Coin Flip Game

A small company is losing money and the boss is looking for ways to cut costs. The boss is a foolish gambler, so he offers two employees the choice of either taking flat 10% pay cut, or playing the following…