Fake Coins Proof

You are a rare coins expert and have determined there are 7 fake coins out of 14 gold coins. Now you need to prove to the judge which ones are fake. It is known that that real coins all weigh…

First to 100

You and a friend play “first to 100”, a game in which you start with 0, and you each take turns adding an integer between 1 and 10 to the sum. Whoever makes the sum reach 100 is the winner.…

Pulley Puzzle

In the pulley puzzle diagram below, there is a pulley attached to a scale. One side of the pulley is attached to a weight and the other side is attached to the ground. If the scale reads 100g, does the…

Escape the Maze

In this maze of 8×8 rooms, each room has an arrow that points up, down, left, or right – and it will only let you move to the adjacent room in the direction of the arrow. After you leave a…

Blue and Red Maze

In this maze, you must alternate going through blue and red doors – in other words, you cannot go through two blue doors in a row or two red doors in a row. Entering through the blue door in the…

Four-Card Problem

You see four cards with A, D, 3, and 6 face-up. You know that each card has a letter on one side and a number on the other side. You are told that cards with a vowel on one side…

3 Digit Code

You have six guesses to figure out a 3 digit code. After each guess, you will be told exactly how many digits are correct but in the wrong place and how many digits are correct and in the right place.…

Tennis in 2 or 3 sets

In a best of 3 tennis match, the player that first wins 2 sets wins the match. For a 3-set tennis match, would you bet on it finishing in 2 or 3 sets? This question was asked in an actual…

Guess the Number

Jake has a 4-digit number in mind and asks Raj to guess the number. Raj can have 7 guesses, and Jake will give him some hints after 6 guesses. Raj makes these 6 guesses: These were all wrong, but Jake…

How to Solve Rebus Puzzles

What are Rebus Puzzles? A rebus is a visual word puzzle that uses the positioning of words, letters, and/or symbols to represent a common phrase, sometimes in an indirect or tricky manner. They are sometimes referred to as “hidden meaning”…

Chess Knight Assassin

From its starting position, the white knight that captured the black queen has moved exactly eight times to get where it is now. How is this possible?

Ants on a Stick

Six ants are walking at 1cm/second on a very narrow stick 100cm long: Ant 1: starts at 0, facing right Ant 2: starts at 20, facing right Ant 3: starts at 30, facing left Ant 4: starts at 40, facing…

Phonetic Alphabet

When someone asks Casey how to spell her name, she helpfully offers: C as in chaos A as in armor S as in scene E as in empire Y as in ? Which is Casey most likely to use as…

Trailing Zeros

How many trailing zeros does 1000! have? “!” is the factorial symbol. For example, 12! = 12 x 11 x 10 x … x 2 x 1 = 479001600, which has 2 trailing zeros (zeros at the end of the…

Polydivisible Number

A polydivisible number is a number for which the first n digits form a number evenly divisible by n for all n between 1 and the number of digits of that number. In other words, the first 2 digits form…

Divisibility Rules

A divisibility rule is a shortcut you can use to see if an integer is evenly divisible by another integer, without doing the actual division. Most divisibility rules involve looking at the digits of the number. Here are some easy…

Confusing Zip Codes

The U.S. uses 5-digit zip codes to help determine where mail goes. Since mail can be oriented in all sorts of directions, they avoid assigning zip codes that could be confused with a different zip code when read upside-down. For…