Easy
Single-insight puzzles accessible with everyday reasoning. One "aha!" moment required.
The Infinite Chocolate Bar
A chocolate bar is cut into five pieces: a small square, a rectangle, two diagonal slope pieces, and a large base piece. We rearrange the pieces, reforming the...
Stack of Coins 1C
You and your friend are really lucky treasure hunters, because you’ve stumbled on another pirate’s treasure: an old chest filled with coins: 149 copper coins...
Stack of Coins 1B
You and your friend stumble on another pirate’s treasure: 99 copper coins and 1 gold coin. As before, these old coins are no longer legal tender, so the copper...
Stack of Coins 1A
You and a friend stumble on a pirate’s treasure: an old chest filled with coins: 19 copper coins and 1 gold coin. These old coins are no longer legal tender,...
Vanishing Square
The diagrams below show two arrangements of the same four pieces. Both form a 13 by 5 right triangle. Yet the first arrangement contains a 1-square-unit gap,...
Brothers and Sisters I Have None
A man is looking at a photograph of someone. His friend asks who it is. The man replies, “Brothers and sisters, I have none. But that man’s father is my...
Ants on a Pole
You have a 1-metre pole with 99 ants placed at each 1-centimetre mark (1cm, 2cm, 3cm, … 99cm). Each ant faces towards the centre of the pole (at the 50cm...
Trailing Zeroes in 100!
How many trailing zeros does 100! have?
Complex Number Multiplication
Consider computing the product of two complex numbers (a + bi) and (c + di) . Using the standard method we learned in school, we get: [Math: (a + bi)(c + di) =...
8 Queens
Can you place 8 queens on a chessboard so that no queen can capture any other queen? Recall that a queen can move any number of squares horizontally,...
9 Dots
You have 9 dots arranged in a 3×3 grid: Without lifting your pen, draw four straight lines that pass through all 9 dots.
Ant in a Cube
An ant is at one corner of a cube with side length 1. The exit is a tiny hole on the corner diagonally opposite the ant. What is the length of the shortest...
Planting Trees 3
The mathematics professor has become your most loyal client. After solving her first two challenges, she calls you back with what she claims is her hardest...
Planting Trees 2
A few weeks after your first job, the mathematics professor calls you back. She was so pleased with your creative solution to the four-tree problem that she...
Planting Trees 1
You are a landscape gardener working on a project for a mathematics professor. She has an unusual request: she wants you to plant four trees in her garden such...
Two Gloves and Three Patients
You’re a surgeon in a remote clinic when three patients arrive requiring emergency operations. Supplies are running low—you rummage through the stockroom but...
Dice Corner
You’re looking through a hole at the corner of a standard die. The image below shows all you can see through the hole: portions of three faces meeting at the...
Coin Weighing 2
Your empire has grown, and now you receive tributes from 9 neighbouring kingdoms. Each kingdom sends a sack of gold coins as a gift. Your advisor suspects that...
Coin Weighing 1
You’re the king of a massive empire. As a gift, a neighbouring kingdom has sent you 9 gold coins. Your advisor suspects that one of the coins is a forgery —...
Equal Shape Cutting 4
With 1 cut, divide the zigzag shape into 2 equal shapes of itself. The cut does not have to be straight, but has to be a connected line. The shapes can be...
Equal Shape Cutting 3
Cut the trapezoid into 4 equal shapes of itself. The shapes can be rotated, but all 4 must be of the same size.
Equal Shape Cutting 2
Cut the L-shape into 4 equal shapes of itself. The shapes can be rotated, but all 4 must be of the same size.
Equal Shape Cutting 1
Cut the triangle into 4 equal shapes of itself. The shapes can be rotated, but all 4 must be of the same size.
Measuring Time with Hourglasses 3
As your cooking skills improve, you decide to try preparing baked salmon fillet. It needs to go into the oven for exactly 20 minutes. As before, you have two...
Measuring Time with Hourglasses 2
After your culinary experience with the soft-boiled eggs, you want to try your hand at cooking a steamed vegetable mix. This time, you need to steam your...
Measuring Time with Hourglasses 1
You’re making the perfect soft-boiled eggs: all you have to do is boil eggs in a pot of water for exactly 9 minutes. However, your kitchen timer is broken, and...
Two Children 2
You’re talking to a different colleague at work when it comes up in the conversation that he has 2 children. “What genders are they?” you ask again. “Well, the...
Two Children 1
You’re talking to your colleague at work when it comes up in the conversation that he has 2 children. “What genders are they?” you ask. “Well, I have at least...
Chain Link 1
Five apprentices are working for you, the village’s master blacksmith. After three days of work, you now have to pay them each a gold chain of 3 links. You...
27 Cubes
A 9cm cube is to be cut into 27 smaller cubes, each of side length 3cm. This can be done with 6 straight cuts to the original cube: 2 parallel cuts along each...
One Less Than a Prime Squared
Show that p^2-1 is always a multiple of 24 if p is a prime that is bigger than 3.
Watermelons Drying in The Sun
A farmer is proud of his newest feat: growing a 120 kg watermelon that he wants to enter in the farming contest next week. Using a special sensor, he detects...
Hummingbird
A train leaves Oakridge at 20 km/h, headed for Fairhaven. At the same time, another train leaves Fairhaven at 30 km/h, headed for Oakridge on the same track....
Close Shave with a Train
Alan is traversing a railway track that spans over a treacherous ravine. As he reaches \frac{3}{8} of the way across the track, he hears the whistle of a train...
The Camel Race
An aging sheikh, nearing the end of his life, decides to leave his vast fortune to one of his two sons. To determine the heir, he devises a strange contest...
Taking Pills
After falling ill, Josh sees a doctor and is prescribed some medication. He is to take 1 pill of Xenoril and 1 pill of Yvexol every 24 hours. The two pills...
Proving Rules on Cards
On the table are 4 cards, each one labelled “A”, “D”, “3”, and “6” respectively. You know that every card has a letter on one side and a number on the other. I...
Marble Pairs
You’re given a jar containing 100 marbles, each one coloured either black or white, and there is at least 1 marble of each colour. You notice that if you pick...
Two Girlfriends and Two Trains
Unfaithful Bob has two girlfriends Alice and Carol. Bob can take a train ride from the city’s train station to get to them. There is only 1 line going in both...
Diagonals on a Cube
Two diagonal lines are drawn on a cube. What is the angle between these two lines?
Guessing Hats 1
Angry with his three wise men, the evil king subjects them to an impossible task: they’ll have to guess the colour of the hats on their heads. If any one of...