Medium
Multi-step puzzles requiring persistence and systematic thinking. High school mathematics sufficient.
Stack of Coins 2
You and your friend have decided to make treasure hunting your weekend project. After a few weeks of treasure hunting, you guys stumble on another pirate’s...
Randomised Ice Cream
For Employee Day, your company is offering everyone free ice cream, and you somehow find yourself at the front of the queue. The vendor manning the ice cream...
The Harmonic Series
Consider the infinite sum: [Math: 1 + \frac{1}{2} + \frac{1}{3} + \frac{1}{4} + \frac{1}{5} + \cdots] This is called the harmonic series. Each term gets...
Coconuts and a Monkey 2
Five people are stranded on a deserted island. They gather a pile of coconuts for food, planning to divide them equally the next morning. However, during the...
Coconuts and a Monkey 1
Ten people are stranded on a deserted island. The gather a pile of coconuts for food, planning to divide them equally the next day. However, that night, one...
L-Shaped Room
We have a room made out of 3 squares arranged in an L shape. Two people are placed randomly within it. What’s the probability that they can see each other?
Unfair Heads and Tails
Player A has n+1 fair coins, while player B has n fair coins. Both players flip all their coins simultaneously and count the number of heads. What is the...
Antipodal Temperature
Assume the Earth is a perfect sphere. Show that at any given time, there exist two antipodal points (points on exact opposite sides of the Earth) with the same...
Pirates and Coins
Five pirates discover a treasure chest containing 100 gold coins. Being logical and ruthless pirates, they must decide how to divide the loot. They follow a...
Poisoned Wine
To celebrate a decade of his rule, the king is holding an extravagant feast, accompanied with 1000 bottles of wine. However, the day before the feast, he...
Poisoned Wine (Extension)
Before the king gets to administer the bottles of wine to the prisoners, an advisor stops him. He says that if more than 8 prisoners die, the townspeople might...
Egg Dropping
For a school project, you’ve devised an egg-protection device — a little contraption that wraps around an egg and is supposed to keep it from breaking when...
Guessing Hats 3
The king’s challenges are growing crueller. This time, three wise men stand in a room, each wearing either a black or white hat chosen at random by a coin...
Guessing Hats 2
The king has grown tired of his wise men outwitting him. This time, he’s devised a more devious challenge. 10 wise men are lined up single file, all facing...
Coin Weighing 3
Your empire has grown even larger. Now 12 neighbouring kingdoms have each sent a single gold coin as tribute. Your advisor suspects that one coin is...
Chomp 3
Even after losing the previous 2 games to you, it appears that your friend has not yet learnt his lesson. This time, he has a rectangular chocolate bar made of...
Chomp 2
After winning the previous game, your friend is back for revenge. This time, he has a chocolate bar made of n by n squares. The same rules apply: You will take...
Chomp 1
You are playing a dangerous game with a friend. He pulls out a chocolate bar comprising 6 squares arranged in a 3 by 2 arrangement. The bottom-left square is...
Two-Bullet Russian Roulette
After offending the toughest guy, Big Billy, at the saloon, he challenges you to a game of Russian Roulette. He takes out a revolver with 6 chambers and loads...
Fastest 3 in 25 Horses
You visit a farm, hoping to buy the 3 fastest horses they have. The farmer says he has 25 horses, but he has no idea how fast each of them are. Instead, he...
Chain Link 2
An apprentice is working for you, the village’s master blacksmith, for 21 days. For payment, you have agreed to give him a gold chain with 21 links, one link...
Confused Bank Teller
When Dorothy went to cash in a cheque, the confused bank teller swapped the dollars and cents. He gave her dollars in place of cents, and cents in place of...
Counting Towns from a Tower
The evil king, no longer trusting his 2 wise men, wants to test their wisdom, so he locks them in a tall tower in the middle of his kingdom. One wise man is...
Average Salaries 1
There’s a global pandemic going on, so everyone is working from home. During this time, 12 employees with similar roles wonder if there are any large salary...
Coins on a Table
You and a friend want to settle who is the smarter of you two with a game. The game is played on a circular table, with you and your friend taking turns to put...
Covering a Chessboard 1
You’re given an 8x8 chessboard with 2 opposite corner tiles removed. You can place dominoes on the board, with each one covering exactly 2 adjacent tiles (you...