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...
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...
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...
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...
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...
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...
Diagonals on a Cube
Two diagonal lines are drawn on a cube. What is the angle between these two lines?
Average Salaries 2
Back in Average Salaries 1, 12 employees came up with a method to find out their average salary without revealing their individual salaries to anyone. Here's...
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...